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

AGENTS.md

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+# PROJECT KNOWLEDGE BASE
+
+**Generated:** 2026-02-19
+**Commit:** a4cff98
+**Branch:** (current)
+
+## OVERVIEW
+
+Homelab topology visualizer - React + Express full-stack app displaying infrastructure as interactive graph (network → hosts → containers → volumes).
+
+## STRUCTURE
+
+```
+./
+├── server/           # Express API backend
+│   └── routes/       # API endpoints (discover, config, stats, files)
+├── src/              # React frontend
+│   ├── components/   # UI components (Header, LeftPanel, RightPanel, Graph)
+│   ├── services/     # Discovery logic
+│   ├── store/        # Zustand state
+│   ├── types/        # TypeScript definitions
+│   └── utils/        # Utilities
+├── docker/           # Nginx + Dockerfile
+├── dist/             # Built frontend (committed - non-standard)
+└── index.html        # Frontend entry
+```
+
+## WHERE TO LOOK
+
+| Task | Location | Notes |
+|------|----------|-------|
+| Add API endpoint | server/routes/*.ts | Modular route files |
+| Add UI component | src/components/*.tsx | React components |
+| State management | src/store/topologyStore.ts | Zustand store |
+| Discovery logic | src/services/discovery.ts | Data transformation |
+| SSH discovery | src/services/sshDiscovery.ts | SSH connectivity |
+
+## CODE MAP
+
+| Symbol | Type | Location | Role |
+|--------|------|----------|------|
+| App | component | src/App.tsx | Main orchestrator |
+| TopologyGraph | component | src/components/Graph/TopologyGraph.tsx | Graph rendering |
+| useTopologyStore | hook | src/store/topologyStore.ts | Global state |
+| discoverRouter | router | server/routes/discover.ts | /api/discover |
+
+## CONVENTIONS (THIS PROJECT)
+
+- **TypeScript**: Strict mode enabled, ESNext modules
+- **Path alias**: `@/*` maps to `src/*`
+- **Frontend**: React 18 + Vite + Tailwind CSS + Zustand
+- **Backend**: Express 5 + TypeScript (tsx runtime)
+- **Graph**: @xyflow/react (React Flow) + dagre layout
+- **Build**: `tsc -b && vite build`
+- **Lint**: `eslint .` (flat config)
+- **Run dev**: `npm run dev` (frontend), `npm run server` (backend)
+
+## ANTI-PATTERNS (THIS PROJECT)
+
+- **DO NOT commit dist/**: Build artifacts in `dist/` are committed - should be in .gitignore
+- **DO NOT skip tsc**: Build script runs `tsc -b` before vite - don't remove
+- **DO NOT use localStorage for SSH credentials**: Security risk (documented in .sisyphus/plans)
+
+## UNIQUE STYLES
+
+- Dual runtime: frontend (Vite) + backend (tsx server/index.ts)
+- Fallback to simulated data if API unavailable
+- Polling-based live updates (configurable interval)
+- Graph auto-layout with dagre
+
+## COMMANDS
+
+```bash
+npm run dev          # Frontend dev server (localhost:3000)
+npm run server       # Backend API server (localhost:3001)
+npm run build        # TypeScript + Vite build
+npm run lint         # ESLint check
+npm run discover     # Run SSH discovery standalone
+```
+
+## NOTES
+
+- Frontend expects API at `http://localhost:3001` (configurable via VITE_API_URL)
+- API routes mounted under `/api/*`
+- CORS configured for `http://localhost:3000` only
+- SSH discovery uses ssh2 library - requires network access to hosts