Add interactive PTY Chat tab with xterm.js terminal emulator

Browser-based interactive terminal sessions with agent CLIs via
WebSocket + node-pty. Supports full TUI rendering (colors, cursor,
ctrl-c) through xterm.js in the browser.

Architecture: xterm.js ←WebSocket→ pty-server.js ←PTY→ agent CLI

- Extract shared buildAgentEnv() from executor into agent-env.ts
- Add internal /api/agents/[id]/env endpoint for PTY server
- Add pty-server.js (WebSocket + node-pty, max 3 sessions, 2hr cleanup)
- Add custom server.js wrapping Next.js with WebSocket upgrade
- Add ChatTab component with agent selector and terminal
- Wire CHAT tab into dashboard nav and render
- Configure serverExternalPackages for node-pty
- Update Dockerfile with build tools and custom server
- Bump k8s memory limit 1Gi → 2Gi for PTY sessions

apps/harness/package.json

@@ -11,17 +11,22 @@
   },
   "dependencies": {
     "@homelab/db": "workspace:^",
+    "@xterm/addon-fit": "^0.11.0",
+    "@xterm/xterm": "^6.0.0",
     "drizzle-orm": "^0.36.0",
     "next": "^15.1.0",
+    "node-pty": "^1.1.0",
     "postgres": "^3.4.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "ws": "^8.20.0",
     "yaml": "^2.7.0"
   },
   "devDependencies": {
     "@types/node": "^22.10.0",
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
+    "@types/ws": "^8.18.1",
     "typescript": "^5.7.0"
   }
 }