feat(page-tags): normalize page_tags onto the shared tags table

page_tags previously stored the tag inline as free-form text — the lone
un-normalized tag concept, while authors/genres/manga-tags all went
through a lookup table + FK. Fold page tags into the SAME shared `tags`
table that manga_tags uses: `page_tags.tag` becomes `page_tags.tag_id`
referencing `tags(id)`. Manga tags and page tags now share one global
vocabulary.

The HTTP contract is unchanged — the API still speaks tag *names*; the
repo resolves name<->id via `repo::tag::upsert_by_name` (the manga-tag
helper) and keeps the stricter page-tag `normalize_tag` at the boundary.
Frontend, DTOs, and response shapes are untouched. User-visible effect:
page-tag names now appear in the manga-tag autocomplete and vice versa.

Migration 0024 backfills `tags` from existing inline values (deduping
case-insensitively), repoints rows, swaps the unique/secondary indexes
to tag_id, and drops the inline column.

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

CLAUDE.md

@@ -136,7 +136,7 @@ docker compose -f docker-compose.dev.yml up -d
 These are first-class slots in the architecture. When adding any of them, plug into the existing seam rather than building parallel infrastructure.
 
 - **Tags / lists**: new tables joined to `mangas`. New `domain`, `repo`, and `api` modules; the existing manga endpoints do not need to change.
-- **Per-page collections / tags**: `collections` is heterogeneous — `collection_mangas` holds whole mangas, `collection_pages` holds individual pages (FK to `pages.id`). Per-user personal page tags live in `page_tags` (distinct from the shared manga `tags` taxonomy; free-form text, normalized at the API layer). Both tables cascade-delete with `pages` and `chapters`, so re-uploading a chapter drops saved-page references by design.
+- **Per-page collections / tags**: `collections` is heterogeneous — `collection_mangas` holds whole mangas, `collection_pages` holds individual pages (FK to `pages.id`). Per-user page tags live in `page_tags`, which references the **shared** `tags` table by `tag_id` (migration 0024) — the same lookup table `manga_tags` uses, so manga tags and page tags share one global vocabulary. The HTTP contract still speaks tag *names*; `repo::page_tag` resolves name↔id via `repo::tag::upsert_by_name` and applies the stricter page-tag `normalize_tag` (lowercase, collapse whitespace, reject wildcards/control/invisible chars) at the API layer. Both `collection_pages` and `page_tags` cascade-delete with `pages` and `chapters`, so re-uploading a chapter drops saved-page references by design.
 - **Tag-based content search (`/search`)**: the user-facing search surface lives at [frontend/src/routes/search/+page.svelte](frontend/src/routes/search/+page.svelte). Three result views (Pages / Chapters / Mangas) consume the matching `/v1/me/page-tags`, `/v1/me/page-tags/chapters`, and `/v1/me/page-tags/mangas` endpoints. Note the two distinct query-param spaces: `?q=` on `/v1/me/page-tags` is a tag-name prefix (for autocomplete in the "Add tag" sheet); `?text=` on the aggregation endpoints is **reserved** for the planned OCR text-search input. Both aggregation handlers accept `text=` on the wire but reject non-empty values with 501 `text_search_not_yet_supported` so adding OCR later doesn't break the API shape. Adding OCR is then: a background worker writes `page_ocr_text` rows, a JOIN on the existing aggregation queries adds the new filter, the `text=` param starts validating instead of rejecting.
 - **Full-text / fuzzy search**: enable `pg_trgm` in a migration and add a GIN index on `mangas.title`; swap the `WHERE` in `repo::manga::list` to use `%` operator or `tsvector`. The API shape (`?search=...`) does not change.
 - **OCR / autotagging**: a background worker (a separate binary or a tokio task spawned in `app::build`) that reads pages from `storage::Storage` and writes tag rows. Do not couple OCR to upload handlers — it runs asynchronously.