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.

internal/store/settings.go

@@ -18,6 +18,7 @@ func (s *Store) GetSettings() (Settings, error) {
 		        traefik_entrypoint, traefik_cert_resolver, traefik_network, traefik_api_url,
 		        image_prune_threshold_mb,
 		        backup_enabled, backup_interval_hours, backup_retention_count,
+		        stats_interval_seconds, stats_retention_hours,
 		        updated_at
 		 FROM settings WHERE id = 1`,
 	).Scan(&st.Domain, &st.ServerIP, &st.PublicIP, &st.Network, &st.SubdomainPattern, &st.NotificationURL,
@@ -29,6 +30,7 @@ func (s *Store) GetSettings() (Settings, error) {
 		&st.TraefikEntrypoint, &st.TraefikCertResolver, &st.TraefikNetwork, &st.TraefikAPIURL,
 		&st.ImagePruneThresholdMB,
 		&backupEnabled, &st.BackupIntervalHours, &st.BackupRetentionCount,
+		&st.StatsIntervalSeconds, &st.StatsRetentionHours,
 		&st.UpdatedAt)
 	if err != nil {
 		return Settings{}, fmt.Errorf("query settings: %w", err)
@@ -65,6 +67,7 @@ func (s *Store) UpdateSettings(st Settings) error {
 			traefik_entrypoint=?, traefik_cert_resolver=?, traefik_network=?, traefik_api_url=?,
 			image_prune_threshold_mb=?,
 			backup_enabled=?, backup_interval_hours=?, backup_retention_count=?,
+			stats_interval_seconds=?, stats_retention_hours=?,
 			updated_at=?
 		 WHERE id = 1`,
 		st.Domain, st.ServerIP, st.PublicIP, st.Network, st.SubdomainPattern, st.NotificationURL,
@@ -76,6 +79,7 @@ func (s *Store) UpdateSettings(st Settings) error {
 		st.TraefikEntrypoint, st.TraefikCertResolver, st.TraefikNetwork, st.TraefikAPIURL,
 		st.ImagePruneThresholdMB,
 		backupEnabled, st.BackupIntervalHours, st.BackupRetentionCount,
+		st.StatsIntervalSeconds, st.StatsRetentionHours,
 		st.UpdatedAt,
 	)
 	if err != nil {