feat: nav counter badges, login backdrop, events i18n + misc fixes

Nav & UI polish
- Sidebar nav items show monospace count badges (projects, sites, stacks,
  proxies). Events badge shows error count only, styled red as actionable
- New $lib/stores/navCounts.ts polls all counts in parallel every 60s and
  refreshes on route change so badges track mutations
- Login page gets a dynamic forge backdrop: rotating conic glow, drifting
  embers, dot-grid texture, vignette — all pure CSS, reduced-motion safe
- main element gets scrollbar-gutter: stable so Settings tab switching no
  longer shifts horizontally when content heights differ

Events i18n
- events.source.* dictionary rewritten to match actually-emitted backend
  sources (deploy, static_site, stale_scanner, stale_cleanup, admin);
  dead keys (container, proxy, system) removed
- EventLogFilter.allSources + /events default sources state updated to match
- Localize "{N} total" via events.totalCount in the page hero toolbar

Backend
- Stage API accepts enable_proxy on create/update (defaults to true) so
  proxy registration can be opted out per stage

Concurrency
- api.ts: queued request waiters no longer double-increment the inflight
  counter; releasing a slot hands it off directly

Reactive effects
- project detail / env / volumes pages wrap side-effect calls in untrack()
  to prevent $effect feedback loops when their loaders mutate tracked state

web/src/routes/events/+page.svelte

@@ -29,7 +29,7 @@
 
 	// Filters
 	let severities = $state<string[]>(['info', 'warn', 'error']);
-	let sources = $state<string[]>(['deploy', 'container', 'proxy', 'system']);
+	let sources = $state<string[]>(['deploy', 'static_site', 'stale_scanner', 'stale_cleanup', 'admin']);
 	let dateRange = $state('all');
 	let searchText = $state('');
 
@@ -216,7 +216,7 @@
 <div class="space-y-4">
 	{#snippet heroToolbar()}
 		{#if stats.total > 0}
-			<span class="forge-pill"><span class="pulse"></span>{stats.total} total</span>
+			<span class="forge-pill"><span class="pulse"></span>{$t('events.totalCount', { count: String(stats.total) })}</span>
 			<button
 				type="button"
 				onclick={() => { showClearConfirm = true; }}