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>

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.63.0",
+  "version": "0.64.0",
   "private": true,
   "type": "module",
   "scripts": {