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/+layout.svelte

@@ -18,7 +18,7 @@
 		providersCache, notificationTrackersCache, trackingConfigsCache,
 		templateConfigsCache, commandConfigsCache, commandTemplateConfigsCache,
 		commandTrackersCache, actionsCache, telegramBotsCache, emailBotsCache,
-		matrixBotsCache, targetsCache,
+		matrixBotsCache, targetsCache, releaseStatusCache,
 	} from '$lib/stores/caches.svelte';
 	import { globalProviderFilter } from '$lib/stores/provider-filter.svelte';
 	import { topbarAction } from '$lib/stores/topbar-action.svelte';
@@ -31,6 +31,17 @@
 
 	let allProviders = $derived(providersCache.items);
 
+	// Sidebar release indicator — reads from the cache populated in onMount.
+	const releaseUpdateAvailable = $derived(!!releaseStatusCache.value?.update_available);
+	// A screen reader hits the brand-version link on every page — keep the
+	// label informative only when an update is available, otherwise announce
+	// the version + product so we don't repeat "Up to date" everywhere.
+	const releaseTooltip = $derived(
+		releaseUpdateAvailable
+			? t('settings.release.updateAvailableTooltip').replace('{v}', releaseStatusCache.value?.latest ?? '')
+			: `Notify Bridge v${__APP_VERSION__}`
+	);
+
 	let providerFilterItems = $derived([
 		{ value: 0, icon: 'mdiFilterOff', label: t('common.allProviders'), desc: '' },
 		...allProviders.map(p => ({ value: p.id, icon: providerDefaultIcon(p), label: p.name, desc: p.type })),
@@ -306,6 +317,7 @@
 				emailBotsCache.fetch(),
 				matrixBotsCache.fetch(),
 				targetsCache.fetch(),
+				releaseStatusCache.fetch(),
 			]).catch(e => console.warn('Failed to load caches for nav counts:', e));
 		}
 	});
@@ -401,7 +413,20 @@
 								{/if}
 								Notify Bridge
 							</h1>
-							<p class="brand-version font-mono">v{__APP_VERSION__}</p>
+							<p class="brand-version font-mono">
+								<a
+									class="brand-version-link"
+									class:has-update={releaseUpdateAvailable}
+									href="/settings#release"
+									aria-label={releaseTooltip}
+									title={releaseUpdateAvailable ? releaseTooltip : undefined}
+								>
+									<span>v{__APP_VERSION__}</span>
+									{#if releaseUpdateAvailable}
+										<span class="brand-version-dot" aria-hidden="true"></span>
+									{/if}
+								</a>
+							</p>
 						</div>
 					</div>
 				{:else}
@@ -772,6 +797,40 @@
 		letter-spacing: 0.02em;
 		font-weight: 500;
 	}
+	.brand-version-link {
+		display: inline-flex;
+		align-items: center;
+		gap: 0.3rem;
+		color: inherit;
+		text-decoration: none;
+		border-radius: 0.3rem;
+		padding: 1px 4px;
+		margin: -1px -4px;
+		transition: color 0.15s, background 0.15s;
+	}
+	.brand-version-link:hover {
+		color: var(--color-foreground);
+		background: var(--color-glass-strong);
+	}
+	.brand-version-link.has-update {
+		color: var(--color-citrus, #d4a73a);
+	}
+	.brand-version-dot {
+		width: 6px;
+		height: 6px;
+		border-radius: 999px;
+		background: var(--color-citrus, #d4a73a);
+		box-shadow: 0 0 6px color-mix(in srgb, var(--color-citrus, #d4a73a) 70%, transparent);
+		animation: brand-version-pulse 2.4s ease-in-out infinite;
+	}
+	@keyframes brand-version-pulse {
+		0%, 100% { transform: scale(1); opacity: 1; }
+		50%      { transform: scale(1.35); opacity: 0.65; }
+	}
+	@media (prefers-reduced-motion: reduce) {
+		.brand-version-dot { animation: none; }
+		.brand-version-link { transition: none; }
+	}
 	.brand-orb {
 		width: 32px; height: 32px;
 		border-radius: 11px;