feat(discover): time-boxed suggestion snooze, server side — #2374

Migration 0049 adds suggestion_snoozes(user_id, candidate_mbid,
candidate_name, snoozed_until), and SuggestArtistsForUser excludes rows
whose snooze hasn't expired.

This is NOT a dislike. Rule #101 forbids a "Not for me" / thumbs-down
UI; a snooze is the approved shape instead because it records no verdict
on the music, expires on its own (~90d), and never reaches the taste
profile. It's acquisition triage — "not right now" — so the filter sits
at the candidate stage rather than in the score, where it would become a
ranking signal by the back door.

Per-user throughout (rule #47): one household member parking a candidate
leaves everyone else's deck untouched.

candidate_name is denormalized because suggestions are out-of-library by
definition — there is no artists row to resolve a display name from, and
the un-snooze list has to show something. That list is why GET
/discover/snoozes exists at all: a parked candidate is by definition
absent from the deck, so without it the DELETE would be unreachable.

Also fixes a hole in the codegen check from #2380: `git diff` ignores
untracked paths, so a brand-new generated file would have passed it
silently. `git add -N` first. This commit is the first to add one.

Endpoints:
  POST   /api/discover/suggestions/{mbid}/snooze  (body: name, days)
  DELETE /api/discover/suggestions/{mbid}/snooze
  GET    /api/discover/snoozes

UI lands in slice 4 (#2375) before any of this merges — rule #27.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

internal/gc/worker.go

@@ -17,6 +17,7 @@
 //   - GcResetStuckSystemPlaylistRuns (#574)
 //   - GcDeleteExpiredPasswordResets   (#575)
 //   - GcPruneDiagnostics              (M9 — diagnostics 30d retention)
+//   - GcDeleteExpiredSuggestionSnoozes (#2374 — snoozes expire, then go)
 package gc
 
 import (
@@ -84,6 +85,7 @@ func (w *Worker) tickOnce(ctx context.Context) {
 	w.runSweep(ctx, "reset_stuck_system_runs", q.GcResetStuckSystemPlaylistRuns)
 	w.runSweep(ctx, "delete_expired_password_resets", q.GcDeleteExpiredPasswordResets)
 	w.runSweep(ctx, "prune_diagnostics", q.GcPruneDiagnostics)
+	w.runSweep(ctx, "delete_expired_suggestion_snoozes", q.GcDeleteExpiredSuggestionSnoozes)
 }
 
 // runSweep is a small adapter so each sweep call site is a one-liner