Add lib/api/routes/tags.js: list + upsert at /api/tags, and an
entity-scoped router mounted at /api/:entity_type/:entity_id/tags
for attach (idempotent), list, and detach. entity_type is bounded by
a zod enum covering space/project/task/page/ref/resource/source_doc/
conversation.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2eb499c56f