feat(search): page content-search endpoint (multi-tag AND + text + warnings)

New GET /v1/me/page-search surfacing the analysis worker's output:

- repo::page_analysis::page_search + PageSearchQuery: multi-tag AND across
  (user page_tags ∪ global page_auto_tags) via the unnest double-negative
  idiom, weighted OCR/scene text ranking (ts_rank over search_doc), and
  content-warning include/exclude. One row per page with is_nsfw +
  deduped content_warnings + rank.
- domain::PageSearchItem.
- api::page_tags: /me/page-search handler with CSV tag/warning parsing
  (parse_tags_csv reuses normalize_tag; parse_warnings_csv validates the
  closed vocabulary), requiring at least one positive filter (422 else).
  This is where the reserved OCR text search lands for pages.

Tests: multi-tag AND user∪auto, speech>sfx ranking, cw include/exclude
(+ row flags), text-only (no tags), missing-filter 422, unknown-warning
422, auth required.

Note: the /me/page-tags/chapters|mangas aggregations keep single-tag
behavior + the reserved text=501 for now; page-level search is the
primary text surface.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1517,7 +1517,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.68.0"
+version = "0.69.0"
 dependencies = [
  "anyhow",
  "argon2",