feat(CUB-58): Agent Status SignalR Service (Angular)

- Scaffold Angular 17 frontend with standalone components
- Add @microsoft/signalr package dependency
- Create AgentStatusService connecting to /hub endpoint
  - Auto-reconnect with progressive delays
  - Listens for AgentStatusChanged and BroadcastMessage
  - Logs all updates to console
  - Exposes statusUpdates$ and connected$ observables
  - onStatusUpdate() alias matching CUB-58 spec
- Create AgentStatusUpdate interface (agentId, status, lastSeenAt)
- Add APP_INITIALIZER provider to start connection on app boot
- Register initializer in app.config.ts
- Update .gitignore for frontend build artifacts

frontend/.editorconfig

@@ -0,0 +1,16 @@
+# Editor configuration, see https://editorconfig.org
+root = true
+
+[*]
+charset = utf-8
+indent_style = space
+indent_size = 2
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.ts]
+quote_type = single
+
+[*.md]
+max_line_length = off
+trim_trailing_whitespace = false