Add paper 解读 (critical review) to Papers UI

[znsoftm]

Add a per-paper 解读 (critical reading) feature on the public Papers catalog so readers can generate, view, and rate a structured Chinese analysis.

UI

• After the arXiv button on each card: 生成解读 / 查看解读 (EN: Generate review / View review)
• Click opens a modal (not a full page) with:
  1. 方法原理与创新
  2. 方法本质
  3. 实验完整性
  4. 论文质量总评
• Star rating 1–5; average and rating count are shown
• Stars stay disabled / locked with a hint while generate is in flight; they enable only after the four sections are displayed
• Generate button shows a loading state while the LLM runs
• ZH/EN i18n; analysis text stays Chinese

API (search-service)

• GET /papers/review/{id} — public review + avg stars (no raw rater list)
• POST /papers/review/{id}/generate — Hub OpenAI-compatible LLM from translate-config.json (same as BabelDOC). Public if the LLM is configured. Idempotent unless force
• POST /papers/review/{id}/rate — {stars:1-5}; upsert by Hub session or anonymous rs_papers_rater cookie
  • 409 review is not ready if no completed review exists (does not create a ratings-only stub)
  • 409 review is still generating if generate is in-flight (fail closed; does not wait on the LLM lock)
• GET /papers/api includes has_review, avg_stars, rating_count

Persistence

• $PAPERS_DIR/reviews/<paper_id>.json (gitignored runtime data)
• Force regenerate keeps existing ratings
• Generate holds a per-id in-flight flag; persist lock is only taken for the short JSON write

Tests

• Average rating upsert (same rater updates, second rater changes avg)
• Generate skips the LLM when a review already exists (unless force)
• Rate-before-review → 409 and no stub file
• Generate then rate → ok
• Rate while generate is in-flight → 409 immediately (fail closed)
• Catalog flags, public GET hides rater keys, anonymous generate + cookie

PDF / translate flows are unchanged. No API keys or review dumps are committed.