feat: deferred dispatch, release-check provider, settings polish

- Defer quiet-hours dispatches into new deferred_dispatch table; drain
  job + periodic catch-up scan re-fire at window end with coalescing on
  (link, event_type, collection_id).
- Add ON DELETE SET NULL migration on event_log_id and partial unique
  index on (link_id, collection_id, event_type) WHERE status='pending'.
- Add release-check provider abstraction (Gitea/GitHub) with SSRF-safe
  URL validation, settings UI cassette, and scheduled polling.
- Replace importlib-only version lookup with version.py helper that
  prefers the higher of installed metadata vs source pyproject so stale
  editable dev installs stop misreporting.
- Aurora frontend polish: MetaStrip component, ReleaseCassette,
  EventDetailModal expansion, and i18n additions.

frontend/src/routes/settings/SettingsHero.svelte

@@ -2,6 +2,7 @@
 	import { onMount, onDestroy } from 'svelte';
 	import { t } from '$lib/i18n';
 	import PageHeader, { type HeaderPill } from '$lib/components/PageHeader.svelte';
+	import { releaseStatusCache } from '$lib/stores/caches.svelte';
 
 	type Tone = 'mint' | 'sky' | 'orchid' | 'coral' | 'citrus' | 'primary';
 
@@ -81,6 +82,19 @@
 			tone: SEVERITY_TONE[lvl] ?? 'mint',
 		});
 
+		const rs = releaseStatusCache.value;
+		if (rs) {
+			if (rs.provider === 'disabled') {
+				out.push({ label: t('settings.release.statusDisabled'), tone: 'sky' });
+			} else if (rs.error && rs.error !== 'provider_changed') {
+				out.push({ label: t('settings.release.statusError'), tone: 'coral' });
+			} else if (rs.update_available && rs.latest) {
+				out.push({ label: `v${rs.latest} ${t('settings.release.heroAvailable')}`, tone: 'citrus' });
+			} else if (rs.latest) {
+				out.push({ label: t('settings.release.statusUpToDate'), tone: 'mint' });
+			}
+		}
+
 		return out;
 	});
 </script>