[Feature] Personalized re-rank and recommendation endpoint

[jerry609]

Source TODO

• 兴趣向量提取
• DailyPaper re-rank
• GET /api/research/recommended
• 前端 为你推荐 区块

Scope

• Interest profile service from feedback + track
• Re-rank formula in daily workflow
• Recommendation API + minimal UI block

Acceptance Criteria

• Recommendations differ by user behavior
• Score composition is observable/debuggable

[jerry609]

Implemented in commit e58161b on branch feat/dailypaper-sse-stream: interest profile service, /api/research/recommended endpoint, DailyPaper personalized rerank hook, and a minimal 'For You' UI block.