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

api/app/schemas/link.py

@@ -0,0 +1,18 @@
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class LinkCreate(BaseModel):
+    name: str
+    url: str
+    description: str | None = None
+    sort_order: int = 0
+
+
+class LinkResponse(LinkCreate):
+    id: int
+    created_at: datetime
+
+    class Config:
+        from_attributes = True