Add Spoiler Flag with veil, AP content-warning encoding, and full-stack plumbing

Authors can flag a review's comment as containing spoilers; the comment is
blurred behind a reveal control for every viewer except the author, omitted
from RSS, and federates as containsSpoilers plus an AP summary content
warning (ADR-0011) so Mastodon-class clients also collapse it. Flag follows
the general-edit path (ADR-0001) across domain, both DB backends, REST,
HTML templates, SPA (shadcn), TUI fixtures, and exports.

README.md

@@ -49,6 +49,7 @@ Open `http://localhost:3000`. The HTTP server and background worker start togeth
 
 - Log movies with a TMDB/OMDb ID or manual title/year/director, with a 1–5 rating and optional watch medium (cinema, streaming, TV, physical media, download, media server)
 - Edit reviews after the fact — update rating, comment, date, or watch medium via partial PATCH; each watch is still a separate record (re-watches tracked)
+- Spoiler Flag — authors mark a review as containing spoilers; the comment is veiled (blur + reveal) for every viewer except the author, withheld from RSS, and federates as `containsSpoilers` + an AP `summary` content warning so Mastodon-style clients also collapse it
 - Background poster fetching and storage (local filesystem or S3-compatible)
 - Movie enrichment via TMDb — full cast, crew, genres, keywords, runtime, budget/revenue, ratings; fetched automatically on movie discovery and refreshed every 30 days; exposed via `GET /api/v1/movies/{id}/profile`
 - Full-text search across movies and people via `GET /api/v1/search` — free-text query plus structured filters (genre, year, person, department, language); backed by SQLite FTS5 or PostgreSQL tsvector + GIN indexes