feat(channel-monitor): request templates with snapshot apply + headers/body override

Problem:
Upstream channels can reject monitor probes based on client fingerprint
(e.g. "only Claude Code clients allowed"). The monitor had no way to
customize the outgoing request to bypass such restrictions.

Solution:
Introduce reusable request templates that carry extra_headers plus an
optional body override; monitors reference a template and receive a
snapshot copy on apply. Template edits do NOT auto-propagate — users
must click "apply to associated monitors" to refresh snapshots, so a
bad template edit cannot instantly break all production monitors.

Data model (migration 112):
- channel_monitor_request_templates: id, name, provider, description,
  extra_headers jsonb, body_override_mode ('off'|'merge'|'replace'),
  body_override jsonb. Unique (provider, name).
- channel_monitors: +template_id (FK, ON DELETE SET NULL), +extra_headers,
  +body_override_mode, +body_override (the three runtime snapshot fields).

Checker (channel_monitor_checker.go):
- callProvider + runCheckForModel accept a CheckOptions carrying the
  snapshot fields. mergeHeaders applies user headers on top of adapter
  defaults (forbidden list: Host / Content-Length / Transfer-Encoding /
  Connection / Content-Encoding).
- buildRequestBody:
    off     -> adapter default body
    merge   -> shallow-merge over default; per-provider deny list
               (model/messages/contents) protects the challenge contract
    replace -> user body verbatim
- Replace mode skips challenge validation; instead HTTP 2xx + non-empty
  extracted response text = operational, empty = failed.
- 4 new unit tests cover all three modes + replace/empty-response case.

Admin API:
- /admin/channel-monitor-templates CRUD + /:id/apply (overwrite snapshot
  on all template_id=id monitors, returns affected count).
- channel_monitor request/response DTOs gain the 4 new fields.

Frontend:
- channelMonitorTemplate.ts API client.
- MonitorAdvancedRequestConfig.vue shared component for headers textarea
  + body mode radio + body JSON editor; used by both template and monitor
  forms.
- MonitorTemplateManagerDialog.vue: provider tabs, list/create/edit/
  delete/apply, live "associated monitors" count per row.
- MonitorFiltersBar: new 模板管理 button next to 新增监控.
- MonitorFormDialog: collapsible 高级 section with template dropdown
  (filtered by form.provider, clears on provider change) + embedded
  AdvancedRequestConfig. Picking a template copies its fields into the
  form (snapshot semantics mirrored on the client).
- i18n zh/en entries for all new copy.

chore: bump version to 0.1.114.32

backend/internal/service/channel_monitor_checker.go

@@ -37,9 +37,23 @@ func newSSRFSafeHTTPClient(timeout time.Duration) *http.Client {
 	return &http.Client{Timeout: timeout, Transport: tr}
 }
 
+// CheckOptions 承载一次检测的自定义入参。
+// 所有字段都是可选（零值即等价于"用默认行为"）。
+type CheckOptions struct {
+	// ExtraHeaders 用户自定义 HTTP 头（merge 到 adapter 默认 headers，用户优先）。
+	ExtraHeaders map[string]string
+	// BodyOverrideMode: off | merge | replace
+	BodyOverrideMode string
+	// BodyOverride 在 merge 模式下做浅合并（key 命中黑名单时静默丢弃），
+	// 在 replace 模式下直接当作完整 body。
+	BodyOverride map[string]any
+}
+
 // runCheckForModel 对单个 (provider, model) 做一次完整检测。
 // 不返回 error：所有失败都包装进 CheckResult.Status=error/failed。
-func runCheckForModel(ctx context.Context, provider, endpoint, apiKey, model string) *CheckResult {
+//
+// opts 承载模板 / 监控快照带来的自定义配置。nil 等同于 "off + 无 extra headers"。
+func runCheckForModel(ctx context.Context, provider, endpoint, apiKey, model string, opts *CheckOptions) *CheckResult {
 	res := &CheckResult{
 		Model:     model,
 		Status:    MonitorStatusError,
@@ -47,9 +61,10 @@ func runCheckForModel(ctx context.Context, provider, endpoint, apiKey, model str
 	}
 
 	challenge := generateChallenge()
+	mode := bodyOverrideMode(opts)
 
 	start := time.Now()
-	respText, rawBody, statusCode, err := callProvider(ctx, provider, endpoint, apiKey, model, challenge.Prompt)
+	respText, rawBody, statusCode, err := callProvider(ctx, provider, endpoint, apiKey, model, challenge.Prompt, opts)
 	latency := time.Since(start)
 	latencyMs := int(latency / time.Millisecond)
 	res.LatencyMs = &latencyMs
@@ -68,22 +83,47 @@ func runCheckForModel(ctx context.Context, provider, endpoint, apiKey, model str
 		return res
 	}
 
+	// Replace 模式：跳过 challenge 校验（用户 body 是静态的，challenge 没法嵌入）。
+	// 改用「HTTP 2xx + 响应文本（adapter.textPath 抽取）非空」作为 operational 判定。
+	// 响应文本为空则降级为 failed（视为上游回了 200 但没实际内容）。
+	if mode == MonitorBodyOverrideModeReplace {
+		if strings.TrimSpace(respText) == "" {
+			res.Status = MonitorStatusFailed
+			res.Message = truncateMessage("replace-mode: upstream returned 2xx with empty text")
+			return res
+		}
+		return finalizeOperationalOrDegraded(res, latency, latencyMs)
+	}
+
 	if !validateChallenge(respText, challenge.Expected) {
 		res.Status = MonitorStatusFailed
 		res.Message = truncateMessage(sanitizeErrorMessage(fmt.Sprintf("challenge mismatch (expected %s, got %q)", challenge.Expected, respText)))
 		return res
 	}
 
+	return finalizeOperationalOrDegraded(res, latency, latencyMs)
+}
+
+// finalizeOperationalOrDegraded 负责走到最后一步的 operational/degraded 判定。
+// 拆出来是为了让 runCheckForModel 不超过 30 行。
+func finalizeOperationalOrDegraded(res *CheckResult, latency time.Duration, latencyMs int) *CheckResult {
 	if latency >= monitorDegradedThreshold {
 		res.Status = MonitorStatusDegraded
 		res.Message = truncateMessage(fmt.Sprintf("slow response: %dms", latencyMs))
 		return res
 	}
-
 	res.Status = MonitorStatusOperational
 	return res
 }
 
+// bodyOverrideMode 归一取 opts.BodyOverrideMode，nil opts / 空串都视为 off。
+func bodyOverrideMode(opts *CheckOptions) string {
+	if opts == nil || opts.BodyOverrideMode == "" {
+		return MonitorBodyOverrideModeOff
+	}
+	return opts.BodyOverrideMode
+}
+
 // pingEndpointOrigin 对 endpoint 的 origin (scheme://host) 发起 HEAD 请求，返回耗时。
 // 失败时返回 nil（不影响主状态判定）。
 func pingEndpointOrigin(ctx context.Context, endpoint string) *int {
@@ -183,29 +223,109 @@ func isSupportedProvider(p string) bool {
 }
 
 // callProvider 通过 providerAdapters 分发到具体实现。
+// opts 承载用户的自定义 headers / body 覆盖（可为 nil）。
 //
 // 返回值：
 //   - extractedText: 按 textPath 抽出的成功文本，仅在 status 2xx 时有意义；非 2xx 时通常为空串
 //   - rawBody: 完整响应体的字符串形式（已被 monitorResponseMaxBytes 截断），用于错误路径保留上游真实回包
 //   - status: HTTP 状态码
 //   - err: 网络 / 序列化错误
-func callProvider(ctx context.Context, provider, endpoint, apiKey, model, prompt string) (extractedText, rawBody string, status int, err error) {
+func callProvider(ctx context.Context, provider, endpoint, apiKey, model, prompt string, opts *CheckOptions) (extractedText, rawBody string, status int, err error) {
 	adapter, ok := providerAdapters[provider]
 	if !ok {
 		return "", "", 0, fmt.Errorf("unsupported provider %q", provider)
 	}
-	body, err := adapter.buildBody(model, prompt)
+	body, err := buildRequestBody(adapter, provider, model, prompt, opts)
 	if err != nil {
-		return "", "", 0, fmt.Errorf("marshal body: %w", err)
+		return "", "", 0, err
 	}
+	headers := mergeHeaders(adapter.buildHeaders(apiKey), opts)
 	full := joinURL(endpoint, adapter.buildPath(model))
-	respBytes, status, err := postRawJSON(ctx, full, body, adapter.buildHeaders(apiKey))
+	respBytes, status, err := postRawJSON(ctx, full, body, headers)
 	if err != nil {
 		return "", "", status, err
 	}
 	return gjson.GetBytes(respBytes, adapter.textPath).String(), string(respBytes), status, nil
 }
 
+// mergeHeaders 把用户自定义 headers 合并到 adapter 默认 headers 上。
+// 用户值覆盖默认；命中黑名单（hop-by-hop / 由 http.Client 自管的）的 key 静默丢弃。
+func mergeHeaders(base map[string]string, opts *CheckOptions) map[string]string {
+	if opts == nil || len(opts.ExtraHeaders) == 0 {
+		return base
+	}
+	out := make(map[string]string, len(base)+len(opts.ExtraHeaders))
+	for k, v := range base {
+		out[k] = v
+	}
+	for k, v := range opts.ExtraHeaders {
+		if IsForbiddenHeaderName(k) {
+			continue
+		}
+		out[k] = v
+	}
+	return out
+}
+
+// buildRequestBody 根据 body_override_mode 构造请求 body。
+//
+//   - off:     adapter 默认 body
+//   - merge:   adapter 默认 body 与 BodyOverride 浅合并；BodyOverride 中命中
+//     bodyMergeKeyDenyList[provider] 的 key 会被静默丢弃，避免破坏 challenge / model 路由
+//   - replace: 直接 marshal BodyOverride 作为完整 body
+//
+// 任何 mode 返回的 []byte 都已经是合法 JSON，可直接送入 postRawJSON。
+func buildRequestBody(adapter providerAdapter, provider, model, prompt string, opts *CheckOptions) ([]byte, error) {
+	mode := bodyOverrideMode(opts)
+
+	if mode == MonitorBodyOverrideModeReplace {
+		if opts == nil || len(opts.BodyOverride) == 0 {
+			return nil, fmt.Errorf("replace mode: body_override is empty")
+		}
+		body, err := json.Marshal(opts.BodyOverride)
+		if err != nil {
+			return nil, fmt.Errorf("marshal body_override (replace): %w", err)
+		}
+		return body, nil
+	}
+
+	defaultBody, err := adapter.buildBody(model, prompt)
+	if err != nil {
+		return nil, fmt.Errorf("marshal default body: %w", err)
+	}
+	if mode != MonitorBodyOverrideModeMerge || opts == nil || len(opts.BodyOverride) == 0 {
+		return defaultBody, nil
+	}
+
+	var defaultMap map[string]any
+	if err := json.Unmarshal(defaultBody, &defaultMap); err != nil {
+		return nil, fmt.Errorf("unmarshal default body for merge: %w", err)
+	}
+	deny := bodyMergeKeyDenyList[provider]
+	for k, v := range opts.BodyOverride {
+		if deny[k] {
+			continue
+		}
+		defaultMap[k] = v
+	}
+	merged, err := json.Marshal(defaultMap)
+	if err != nil {
+		return nil, fmt.Errorf("marshal merged body: %w", err)
+	}
+	return merged, nil
+}
+
+// bodyMergeKeyDenyList 在 merge 模式下，禁止用户覆盖这些 provider-specific 的关键字段。
+// 思路抄 check-cx 的 EXCLUDED_METADATA_KEYS：保护 challenge / model 路由不被用户误伤。
+// 用户想动这些字段就用 replace 模式（已知会跳 challenge 校验）。
+//
+//nolint:gochecknoglobals // 静态查表，初始化后不变。
+var bodyMergeKeyDenyList = map[string]map[string]bool{
+	MonitorProviderOpenAI:    {"model": true, "messages": true, "stream": true},
+	MonitorProviderAnthropic: {"model": true, "messages": true},
+	MonitorProviderGemini:    {"contents": true},
+}
+
 // postRawJSON 发送 POST + 已序列化好的 JSON 字节，限制响应体大小，返回响应字节、HTTP status、错误。
 // adapter 自行 marshal 是为了精确控制字段顺序与类型，所以这里直接收 []byte 而不是 any。
 func postRawJSON(ctx context.Context, fullURL string, payload []byte, headers map[string]string) ([]byte, int, error) {