fix: harden security, fix concurrency bugs, and address review findings

Security:
- rate limit /api/webhook routes per-IP and cap concurrent site syncs
- global SSE connection cap (256) with new sse_gate
- validate ?tail= and cap JSON log responses at 4 MiB
- strip ANSI/CSI/OSC and control bytes from streamed log lines
- redact webhook secret from request log middleware
- scrub host details from /api/health for non-admin viewers
- drop container_id from /api/system/stats/top for non-admins
- generate webhook secrets via crypto/rand; require >=32 chars on insert
- verify iid path consistency in streamContainerLogs
- LimitReader on site webhook body; reject malformed non-empty bodies

Concurrency / correctness:
- stats collector: Stop() no longer hangs without Start(), semaphore
  acquired in parent loop so ctx cancellation short-circuits the queue,
  in-flight tick cancellable via shared base context, zero-ts guard
- webhook handler: replace fire-and-forget goroutine with WaitGroup-tracked
  workers + Drain() wired into graceful shutdown
- $derived(() => ...) mis-idiom fixed in ContainerStats / InstanceCard /
  ProjectCard (returned function instead of value)
- SystemResourcesCard: rename `window` and `t` locals to avoid shadowing
  globalThis.window and the i18n `t` import

Quality / performance:
- replace O(n^2) insertion sort with sort.Slice in stats top
- runMigrations only swallows duplicate-column / already-exists errors
- PruneStatsSamplesBefore wrapped in a transaction
- collapse N+1 in unusedImageStats / pruneImages to one ListAllInstances
  pass; surface DB errors instead of silently treating them as inactive
- run Docker Info + DiskUsage in parallel via errgroup
- container log SSE emits `: ping` heartbeat every 20 s
- imageMatches case-insensitive on registry host (RFC behaviour)
- log warning on invalid stage tag pattern instead of silent skip
- reject malformed non-empty site webhook payloads

Frontend / i18n:
- shared formatBytes utility replaces three local copies
- statsInterval store drives dynamic "no samples / collection disabled"
  copy across ContainerStats and SystemResourcesCard
- top consumers row now shows owner_name (project/stage or site name)
- drop seven `as any` casts on the Settings type; add cloudflare_api_token
  write-only field
- move "Service status", "Docker daemon", "Docker unreachable",
  "Proxy unreachable", "reachable", and "Docker daemon is not reachable."
  strings into en/ru i18n bundles

web/src/lib/components/SystemDaemonsCard.svelte

@@ -36,12 +36,11 @@
 		totalContainers > 0 ? ((docker?.stopped ?? 0) / totalContainers) * 100 : 0
 	);
 
+	import { formatBytes as formatBytesShared } from '$lib/format/bytes';
+
 	function formatBytes(n: number | undefined): string {
 		if (!n || n <= 0) return '—';
-		const gb = n / 1024 ** 3;
-		if (gb >= 1) return `${gb.toFixed(1)} GB`;
-		const mb = n / 1024 ** 2;
-		return `${mb.toFixed(0)} MB`;
+		return formatBytesShared(n);
 	}
 
 	function formatMs(n: number | undefined): string {
@@ -95,7 +94,7 @@
 				</div>
 			{:else if !dockerConnected}
 				<div class="panel-error">
-					<code>{docker?.error ?? 'Docker daemon is not reachable.'}</code>
+					<code>{docker?.error ?? $t('daemons.dockerNotReachable')}</code>
 					<p>{$t('daemons.dockerHint')}</p>
 				</div>
 			{:else}