Non-admin GET /api/v1/prompts/tags went through get_prompts_by_user_id,
which loaded every active prompt with its full content/data/meta plus
owner records and all access grants, then ran one has_access query per
prompt that wasn't owned by the caller - all so the endpoint could
collapse the result to a sorted tag list. With 600 prompts this took
several seconds while the admin path (a single SELECT) returned in <1s.
Add Prompts.get_tags_by_user_id which selects only the tags column and
applies the same EXISTS-based access filter used by /list. Also tighten
the admin get_tags to project just the tags column instead of full rows.
The endpoint is now one DB query (plus one for groups), no row hydration,
no N+1.
Co-authored-by: Claude <noreply@anthropic.com>
