feat(stats): resource metrics dashboard + sites logs/stats

Background collector samples CPU/memory/network/block I/O for every
instance and site on a configurable interval (default 15s, range
5-300s), persists samples to SQLite with a configurable retention
window (default 2h, range 0-24h), and skips ticks gracefully when
the Docker daemon is unreachable. Settings are reloadable without
a restart — each tick re-reads them.

New API endpoints:
- GET /api/system/stats (host snapshot: info + df)
- GET /api/system/stats/history
- GET /api/system/stats/top?by=cpu|memory
- GET /api/projects/{id}/stages/{s}/instances/{iid}/stats/history
- GET /api/sites/{id}/stats[/history]
- GET /api/sites/{id}/logs (SSE + JSON, reuses instance log streamer)

Frontend:
- ECharts added with tree-shaken imports (~180KB gzip) for
  future-proof time-series/gantt/graph visualizations
- CollapsibleSection wraps all dashboard sections (system health,
  daemons, system resources, static sites, projects) with
  localStorage-persisted open state
- SystemResourcesCard shows capacity tiles, workload utilization
  chart with 30m/2h/6h/24h window picker, disk breakdown with
  reclaimable callouts, and top 5 consumers
- ContainerStats and ContainerLogs take a source discriminated union
  so sites reuse the same components as instances; sites detail page
  embeds both for Deno backend debugging
- Settings › Maintenance exposes collection interval + retention
- Docker-unavailable state returns 503 and renders an amber banner
  instead of a generic 500

Full i18n coverage (en + ru) for all new strings.

cmd/server/main.go

@@ -33,6 +33,7 @@ import (
 	"github.com/alexei/tinyforge/internal/registry"
 	"github.com/alexei/tinyforge/internal/stale"
 	"github.com/alexei/tinyforge/internal/stack"
+	"github.com/alexei/tinyforge/internal/stats"
 	"github.com/alexei/tinyforge/internal/staticsite"
 	"github.com/alexei/tinyforge/internal/store"
 	"github.com/alexei/tinyforge/internal/webhook"
@@ -276,6 +277,12 @@ func main() {
 	}
 	scheduleAutobackup(settings.BackupEnabled, settings.BackupIntervalHours)
 
+	// Initialize resource stats collector. Interval + retention are read from
+	// settings on each tick, so configuration changes take effect within one
+	// tick without a restart.
+	statsCollector := stats.New(db, dockerClient)
+	statsCollector.Start()
+
 	// Initialize static site manager and health checker.
 	staticSiteMgr := staticsite.NewManager(db, dockerClient, proxyProvider, eventBus, encKey)
 	webhookHandler.SetSiteSyncTriggerer(staticSiteMgr)
@@ -364,6 +371,7 @@ func main() {
 	staticSiteHealth.Stop()
 	staleScanner.Stop()
 	poller.Stop()
+	statsCollector.Stop()
 
 	// Drain in-progress deploys and notifications.
 	dep.Drain()