Add HDFS browser, SSH terminal, presentation editor, lab health panel

- HDFS WebHDFS file browser (api/hdfs_api.py + HdfsView)
- In-browser SSH terminal via paramiko WebSocket bridge (api/ssh_terminal.py + SshTerminal, xterm.js)
- Presentation deck editor (text + image upload) and CRUD endpoints
- Collapsible GPU matrix + new LabHealthPanel in SideNav
- Topology fixes (edge alignment, Hadoop node, compact nodes)
- nginx ws timeout bump for long-lived SSH sessions

ui/package.json

@@ -10,6 +10,8 @@
   },
   "dependencies": {
     "@tanstack/react-query": "^5.62.8",
+    "@xterm/xterm": "^5.5.0",
+    "@xterm/addon-fit": "^0.10.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^0.469.0",