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/models/link.py

@@ -0,0 +1,14 @@
+from sqlalchemy import Column, Integer, String, DateTime
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class Link(Base):
+    __tablename__ = "links"
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    name = Column(String(100), nullable=False)
+    url = Column(String(500), nullable=False)
+    description = Column(String(200), nullable=True)
+    sort_order = Column(Integer, default=0)
+    created_at = Column(DateTime, default=func.now())