feat: container logs viewer with SSE streaming and line limiter

- Add GET /api/projects/{id}/stages/{stage}/instances/{iid}/logs endpoint
- Supports JSON mode (returns array of lines) and SSE mode (streams in real-time)
- Docker log stream header (8-byte prefix) stripped automatically
- ContainerLogs component with:
  - Tail line selector (50/200/500/1000)
  - Follow button for real-time streaming via SSE
  - Auto-scroll to bottom
  - Dark terminal-style display
  - Close button
- Logs button (events icon) on each instance card
- i18n keys in EN and RU

internal/api/router.go

@@ -204,6 +204,7 @@ 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}/logs", s.streamContainerLogs)
 				r.Get("/images", s.listProjectImages)
 				r.Get("/volumes", s.listVolumes)
 				r.Get("/volumes/{volId}/browse", s.browseVolume)