feat(tags): official/curated tag vocabulary (Tag.isOfficial + staff curation routes)

[obrien-k]

What

Tag aliases are live (tag.ts + tagAliases, integration-tested) and act as the upload normalizer, but there is no curated "official tags" vocabulary — nothing distinguishes the canonical browse/discovery tag set from freeform member tags.

Scope

• Tag.isOfficial flag + staff promote/demote routes (permission-gated), admin-page section for curation.
• Alias table remains the normalizer; official flags are curation on top, not a replacement.

Design blueprint exists (2026-07-04 parity deep dive, item J6).

Surfaced by the 2026-07-08 parity harvest.

[obrien-k]

Blueprint detail (deep-scrub item J6), as promised in the body:

• Schema: Tag.isOfficial Boolean @default(false) + index (migration add_tag_is_official).
• Routes: GET /api/tags?official=1; PUT /api/tags/:id/official (tags_manage, audit tag.official_changed).
• Upload normalization already flows through resolveTagNames — no change in v1 (the alias table stays the normalizer).
• UI: a section on the tag-alias admin page.
• A genre/other tag-type split was considered and dropped — no consumer.