feat: add password authentication support (closes #7)

Add token/password auth mode toggle on the login screen.
When password mode is selected, sends { password } instead of
{ token } in the WebSocket connect handshake.

Also adds clipboard utility tests and fixes credential test
to include authMode field.

package.json

@@ -60,6 +60,7 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.0",
     "globals": "^16.5.0",
+    "jsdom": "^28.1.0",
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.55.0",
     "vite": "^7.3.1",