Workspace Terminal tab: xterm front end + short-lived token route

- New Terminal tab in the workspace shell, backed by xterm.js, that connects
  to the worker's PTY WebSocket using a short-lived token minted by
  /api/agent-jobs/:id/terminal-token (owner-auth'd, never exposes the worker
  secret to the browser)
- Site-matched xterm theme (light/dark, live theme switching), Victor Mono,
  binary stdin + JSON resize protocol, reconnect, graceful 'not configured'
  state when NEXT_PUBLIC_SPOON_AGENT_WORKER_WS_URL is unset
- env: NEXT_PUBLIC_SPOON_AGENT_WORKER_WS_URL (client), SPOON_AGENT_TERMINAL_SECRET

bun.lock

@@ -107,6 +107,9 @@
         "@spoon/backend": "workspace:*",
         "@spoon/ui": "workspace:*",
         "@t3-oss/env-nextjs": "^0.13.11",
+        "@xterm/addon-fit": "^0.11.0",
+        "@xterm/addon-web-links": "^0.12.0",
+        "@xterm/xterm": "^6.0.0",
         "convex": "catalog:convex",
         "monaco-editor": "latest",
         "monaco-vim": "latest",
@@ -1689,6 +1692,12 @@
 
     "@xmldom/xmldom": ["@xmldom/xmldom@0.8.11", "", {}, "sha512-cQzWCtO6C8TQiYl1ruKNn2U6Ao4o4WBBcbL61yJl84x+j5sOWWFU9X7DpND8XZG3daDppSsigMdfAIl2upQBRw=="],
 
+    "@xterm/addon-fit": ["@xterm/addon-fit@0.11.0", "", {}, "sha512-jYcgT6xtVYhnhgxh3QgYDnnNMYTcf8ElbxxFzX0IZo+vabQqSPAjC3c1wJrKB5E19VwQei89QCiZZP86DCPF7g=="],
+
+    "@xterm/addon-web-links": ["@xterm/addon-web-links@0.12.0", "", {}, "sha512-4Smom3RPyVp7ZMYOYDoC/9eGJJJqYhnPLGGqJ6wOBfB8VxPViJNSKdgRYb8NpaM6YSelEKbA2SStD7lGyqaobw=="],
+
+    "@xterm/xterm": ["@xterm/xterm@6.0.0", "", {}, "sha512-TQwDdQGtwwDt+2cgKDLn0IRaSxYu1tSUjgKarSDkUM0ZNiSRXFpjxEsvc/Zgc5kq5omJ+V0a8/kIM2WD3sMOYg=="],
+
     "@xtuc/ieee754": ["@xtuc/ieee754@1.2.0", "", {}, "sha512-DX8nKgqcGwsc0eJSqYt5lwP4DH5FlHnmuWWBRy7X0NcaGR0ZtuyeESgMwTYVEtxmsNGY+qit4QYT/MIYTOTPeA=="],
 
     "@xtuc/long": ["@xtuc/long@4.2.2", "", {}, "sha512-NuHqBY1PB/D8xU6s/thBgOAiAP7HOYDQ32+BFZILJ8ivkUkAHQnWfn6WhL79Owj1qmUnoN/YPhktdIoucipkAQ=="],