feat(server/coverart): auto-bump version on registered-provider change

On boot, the SettingsService computes a SHA-256 hash of the sorted
registered-provider IDs and compares to the hash stored on
cover_art_sources_meta. Mismatch → atomic bump of current_version +
update of stored hash. The next enrichment pass picks up the new
version, all 'none' rows become eligible, and they get retried
against the new chain (now including Deezer / Last.fm).

One-shot: subsequent boots without a provider-set change don't bump
again. The check is best-effort — failures are logged at Warn but
don't refuse startup; a temporarily unreachable DB at boot just
means 'none' rows stay parked until a manual re-search (next task).

Tests cover first-boot (empty stored hash → bump), repeat-boot
(no change → no bump), and the registered-providers-hash
determinism.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/minstrel/main.go

@@ -90,6 +90,12 @@ func run() error {
 		logger.Error("coverart settings service init failed", "err", err)
 		os.Exit(1)
 	}
+	if newVer, bumped, berr := coverSettings.BumpVersionIfProvidersChanged(ctx); berr != nil {
+		logger.Warn("coverart: provider-hash boot check failed", "err", berr)
+	} else if bumped {
+		logger.Info("coverart: registered provider set changed; version bumped",
+			"new_version", newVer)
+	}
 	coverEnricher := coverart.NewEnricher(pool, logger.With("component", "coverart"), coverSettings)
 	coverEnricher.DataDir = cfg.Storage.DataDir