feat: expand discovery with systemd services, LXC/VMs, SSH terminal, and filebrowser

- Add systemd service discovery to backend
- Add Proxmox LXC/VM detection
- Add hostType field to config for better host categorization
- Fix SSH trust between hosts (ubuntu/grizzley -> truenas/proxmox)
- Add SSH terminal support via xterm.js
- Add filebrowser for browsing host filesystems
- Update frontend types and components for new node types

server/AGENTS.md

@@ -0,0 +1,60 @@
+# Server (Express API Backend)
+
+**Generated:** 2026-02-19
+**Location:** server/
+
+## OVERVIEW
+
+Express 5 + TypeScript backend serving REST API endpoints for homelab topology discovery.
+
+## STRUCTURE
+
+```
+server/
+├── index.ts         # Express app entry, CORS, route mounting
+├── config.ts        # Server configuration
+├── types.ts         # Shared TypeScript types
+├── config.json      # Runtime config (contains hosts, credentials)
+├── config.example.json
+└── routes/          # API endpoints
+    ├── discover.ts  # POST /api/discover - SSH discovery
+    ├── config.ts    # GET/PUT /api/config
+    ├── stats.ts     # GET /api/stats
+    └── files.ts     # GET /api/files
+```
+
+## WHERE TO LOOK
+
+| Task | File | Notes |
+|------|------|-------|
+| Add new endpoint | server/routes/{name}.ts | Create router, import in index.ts |
+| Modify CORS | server/index.ts | CORS middleware (line 12-15) |
+| Change port | server/index.ts | PORT const (line 9) |
+
+## CONVENTIONS
+
+- **Route files**: Export default router, mount in index.ts via `app.use('/api', router)`
+- **Error handling**: Return JSON `{ error: string }` on failure
+- **Config**: Use server/config.ts for shared config, not hardcode
+- **Credentials**: Never log or expose SSH credentials in responses
+
+## ANTI-PATTERNS
+
+- **NEVER expose SSH credentials in API responses**
+- **DO NOT store credentials in source** - use server/config.json
+
+## API ENDPOINTS
+
+| Method | Path | Purpose |
+|--------|------|---------|
+| POST | /api/discover | Run SSH discovery on hosts |
+| GET | /api/config | Get configuration |
+| PUT | /api/config | Update configuration |
+| GET | /api/stats | Get statistics |
+| GET | /api/files | Get file topology |
+
+## NOTES
+
+- Server runs on port 3001
+- CORS allows only `http://localhost:3000`
+- Health check: GET /api/health