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/api/router.go

@@ -219,6 +219,7 @@ func (s *Server) Router() chi.Router {
 				r.Get("/stages/{stage}/env", s.listStageEnv)
 				r.Get("/stages/{stage}/instances", s.listInstances)
 				r.Get("/stages/{stage}/instances/{iid}/stats", s.getInstanceStats)
+				r.Get("/stages/{stage}/instances/{iid}/stats/history", s.getInstanceStatsHistory)
 				r.Get("/stages/{stage}/instances/{iid}/logs", s.streamContainerLogs)
 				r.Get("/images", s.listProjectImages)
 				r.Get("/volumes", s.listVolumes)
@@ -288,6 +289,9 @@ func (s *Server) Router() chi.Router {
 				r.Get("/", s.getStaticSite)
 				r.Get("/secrets", s.listStaticSiteSecrets)
 				r.Get("/storage", s.getStaticSiteStorage)
+				r.Get("/logs", s.streamStaticSiteLogs)
+				r.Get("/stats", s.getStaticSiteStats)
+				r.Get("/stats/history", s.getStaticSiteStatsHistory)
 
 				// Admin-only mutations.
 				r.Group(func(r chi.Router) {
@@ -333,6 +337,11 @@ func (s *Server) Router() chi.Router {
 			// Stale container endpoints (read).
 			r.Get("/containers/stale", s.listStaleContainers)
 
+			// System resources (read-only).
+			r.Get("/system/stats", s.getSystemStats)
+			r.Get("/system/stats/history", s.getSystemStatsHistory)
+			r.Get("/system/stats/top", s.listTopContainersByCPU)
+
 			// Admin-only routes: require admin role.
 			r.Group(func(r chi.Router) {
 				r.Use(auth.AdminOnly)