fix(openai): gate Codex image bridge injection

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/service/codex_image_generation_bridge.go

@@ -0,0 +1,64 @@
+package service
+
+import "strings"
+
+const featureKeyCodexImageGenerationBridge = "codex_image_generation_bridge"
+
+func boolOverridePtr(v bool) *bool {
+	return &v
+}
+
+func boolOverrideFromMap(values map[string]any, keys ...string) *bool {
+	if values == nil {
+		return nil
+	}
+	for _, key := range keys {
+		if v, ok := values[key].(bool); ok {
+			return boolOverridePtr(v)
+		}
+	}
+	return nil
+}
+
+func platformBoolOverride(values map[string]any, key string, platform string) *bool {
+	if values == nil {
+		return nil
+	}
+	if v, ok := values[key].(bool); ok {
+		return boolOverridePtr(v)
+	}
+	raw, ok := values[key].(map[string]any)
+	if !ok {
+		return nil
+	}
+	platform = strings.TrimSpace(platform)
+	if platform == "" {
+		return nil
+	}
+	if v, ok := raw[platform].(bool); ok {
+		return boolOverridePtr(v)
+	}
+	return nil
+}
+
+// CodexImageGenerationBridgeOverride returns the channel-level override for Codex
+// image_generation bridge injection. Nil means follow the global/account policy.
+func (c *Channel) CodexImageGenerationBridgeOverride(platform string) *bool {
+	if c == nil {
+		return nil
+	}
+	return platformBoolOverride(c.FeaturesConfig, featureKeyCodexImageGenerationBridge, platform)
+}
+
+// CodexImageGenerationBridgeOverride returns the account-level override for Codex
+// image_generation bridge injection. Nil means follow the channel/global policy.
+func (a *Account) CodexImageGenerationBridgeOverride() *bool {
+	if a == nil || a.Platform != PlatformOpenAI || a.Extra == nil {
+		return nil
+	}
+	if override := boolOverrideFromMap(a.Extra, featureKeyCodexImageGenerationBridge, "codex_image_generation_bridge_enabled"); override != nil {
+		return override
+	}
+	openaiConfig, _ := a.Extra[PlatformOpenAI].(map[string]any)
+	return boolOverrideFromMap(openaiConfig, featureKeyCodexImageGenerationBridge, "codex_image_generation_bridge_enabled")
+}