feat: builder 简历生成 + 轻度优化 + 简历导入交付副本

自内部仓库剥离深度优化与 RAG 知识库后的交付版本：
- Builder 对话式简历生成（FSM + 意图路由 LLM 兜底增强）
- 条目级轻度优化：事实覆盖门禁 + STAR/bullet 修复链，功能/简介/成果与技术栈同级保护
- 简历导入：DOCX/PDF 解析、结构归一、手机号脱敏
- PostgreSQL 运行时 + Alembic 迁移链

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/rate_limit.py

@@ -0,0 +1,37 @@
+"""In-process sliding-window rate limiting for single-process deployments."""
+
+from __future__ import annotations
+
+import time
+from collections import deque
+from typing import Callable
+
+
+class SlidingWindowRateLimiter:
+    """Allow at most ``limit`` requests per key during a sliding time window."""
+
+    def __init__(
+        self,
+        *,
+        limit: int,
+        window_seconds: float,
+        clock: Callable[[], float] = time.monotonic,
+    ) -> None:
+        if limit < 1:
+            raise ValueError("limit must be positive")
+        if window_seconds <= 0:
+            raise ValueError("window_seconds must be positive")
+        self.limit = limit
+        self.window_seconds = window_seconds
+        self.clock = clock
+        self._hits: dict[str, deque[float]] = {}
+
+    def allow(self, key: str) -> bool:
+        now = self.clock()
+        hits = self._hits.setdefault(key, deque())
+        while hits and now - hits[0] >= self.window_seconds:
+            hits.popleft()
+        if len(hits) >= self.limit:
+            return False
+        hits.append(now)
+        return True