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

web/src/lib/i18n/en.json

@@ -680,6 +680,14 @@
     "route": "route",
     "routes": "routes"
   },
+  "logs": {
+    "title": "Container Logs",
+    "lines": "lines",
+    "follow": "Follow",
+    "following": "Following...",
+    "loading": "Loading logs...",
+    "noLogs": "No log output"
+  },
   "events": {
     "title": "Event Log",
     "noEvents": "No events found",