fix: resolve 10 code review issues

High priority:
- Fix concurrent race condition for view_count/like_count (atomic update)
- Add route request ID tracking to prevent race conditions
- Filter get_joke by status=approved (no pending content leak)
- Add error feedback for like button

Performance:
- Optimize random joke query (avoid full table sort)
- Limit page_size max to 100 (DoS prevention)

Medium:
- Add localStorage quota error handling
- Handle empty AI response gracefully
- Fix generate content title extraction

Low:
- Add rejected_jokes to stats API
- Update dashboard to show rejected count

crawler/ai_service.py

@@ -0,0 +1,71 @@
+"""LLM 处理：调用 NVIDIA NIM（OpenAI 兼容 API）进行笑话提取、改写和分类。"""
+
+import json
+import os
+from openai import OpenAI
+
+
+class AiService:
+    def __init__(self, api_base: str, api_key: str, model_name: str, temperature: float = 0.7, max_tokens: int = 2048):
+        self.client = OpenAI(base_url=api_base, api_key=api_key)
+        self.model = model_name
+        self.temperature = temperature
+        self.max_tokens = max_tokens
+
+    def extract_jokes(self, page_content: str, known_types: list[str], known_crowds: list[str]) -> list[dict]:
+        """从页面内容中提取笑话，返回结构化数据。"""
+        from crawler.prompts import EXTRACTION_SYSTEM_PROMPT, EXTRACTION_USER_PROMPT
+
+        user_prompt = EXTRACTION_USER_PROMPT.format(
+            page_content=page_content[:8000],
+            known_types=", ".join(known_types),
+            known_crowds=", ".join(known_crowds),
+        )
+
+        response = self.client.chat.completions.create(
+            model=self.model,
+            messages=[
+                {"role": "system", "content": EXTRACTION_SYSTEM_PROMPT},
+                {"role": "user", "content": user_prompt},
+            ],
+            temperature=self.temperature,
+            max_tokens=self.max_tokens,
+        )
+
+        raw = response.choices[0].message.content
+        return self._parse_json(raw)
+
+    def rewrite_joke(self, content: str) -> str:
+        """润色单条笑话内容。"""
+        from crawler.prompts import REWRITE_SYSTEM_PROMPT, REWRITE_USER_PROMPT
+
+        response = self.client.chat.completions.create(
+            model=self.model,
+            messages=[
+                {"role": "system", "content": REWRITE_SYSTEM_PROMPT},
+                {"role": "user", "content": REWRITE_USER_PROMPT.format(content=content)},
+            ],
+            temperature=0.8,
+            max_tokens=500,
+        )
+        return response.choices[0].message.content.strip()
+
+    def _parse_json(self, raw: str) -> list[dict]:
+        """安全解析 LLM 返回的 JSON。"""
+        try:
+            data = json.loads(raw)
+            if isinstance(data, dict):
+                jokes = data.get("jokes") or data.get("items") or [data]
+            else:
+                jokes = data
+            return [j for j in jokes if isinstance(j, dict) and j.get("content")]
+        except json.JSONDecodeError:
+            # 尝试提取 markdown 代码块
+            if "```json" in raw:
+                raw = raw.split("```json")[1].split("```")[0]
+            elif "```" in raw:
+                raw = raw.split("```")[1].split("```")[0]
+            try:
+                return json.loads(raw.strip())
+            except Exception:
+                return []