feat(web): 红果-style homepage + instant-play prebaked first acts

Rewrites all 64 homepage cards (32 男性向 + 32 女性向) as short-drama hook
stories (战神归来 / 重生分手前夜 / 系统选妃 / 穿成乙游男配 / 末世异能 / 民国
谍战 / 修真渡劫 …) and regenerates each cover via FLUX in its assigned art
style (12 styles spread across 64 cards) at 832×1024 ≈4:5.

Click-to-play path: cards now jump straight to /play?card=<name> and hydrate
Session from /home/firstact/<name>.json — the engine pipeline (Architect +
Writer + CharacterDesigner + Painter) has been pre-run for 44/64 cards. The
remaining 20 (m14/m29/f14..f31) are pending an LLM credit top-up; their
clicks fall through to live /api/start for now.

Runware-hosted first-scene images are downloaded into /home/firstscene/
and the JSONs are rewritten to point at the local webp, so click → first
image is bounded by local-disk decode (~100ms) instead of CDN round-trip.

Scripts:
- scripts/generate-home-images.mjs  — rewrites all 64 cover prompts, per-card
  styles baked into prompts, 832×1024 dims to match StoryCard aspect
- scripts/prebake-firstacts.mjs     — POST /api/start × 64 with concurrency
  4, saves StartResponse to public/home/firstact/<name>.json
- scripts/localize-firstact-images.mjs — downloads each prebaked imageUrl
  to public/home/firstscene/<name>.webp (q80, ≤1600px) and rewrites JSON

README: adds Screenshots section (3×3 gallery) to README.md / README.zh-CN.md,
9 in-game shots compressed to docs/screenshots/*.webp (7.5MB → 680KB).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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