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/lib/api.ts

@@ -57,7 +57,10 @@ function acquireSlot(signal?: AbortSignal | null): Promise<void> {
 		return Promise.resolve();
 	}
 	return new Promise<void>((resolve, reject) => {
-		const entry = () => { inflight++; resolve(); };
+		// A queued waiter inherits the releasing request's slot, so it
+		// must not increment `inflight` again — `releaseSlot` skips the
+		// decrement when it hands the slot off, keeping the count stable.
+		const entry = () => { resolve(); };
 		queue.push(entry);
 
 		signal?.addEventListener('abort', () => {