Adds GET /community/posts, GET /community/posts/{slug}, GET /community/feed.rss,
GET /community/local-feed, POST /community/posts, DELETE /community/posts/{slug},
POST /community/posts/{slug}/fork, and POST /community/posts/{slug}/fork-adapt (501 stub).
Wires init_community_store into main.py lifespan. 7 new tests; 115 total passing.
Uses circuitforge_core.tasks.scheduler. VRAM detection via cf-orch when
available, falling back to unlimited. Adds expiry_llm_fallback task type
to background-predict expiry dates for items the LUT doesn't cover.
