style: fix all ruff and eslint errors across codebase

Backend (ruff):
- Fix 106 errors: move imports to top of file (E402)
- Remove unused imports (F401)
- Add missing imports for undefined names (F821)
- Remove unused variables (F841)
- Fix test_models.py broken RefreshToken test
- Fix test_projects_api.py missing TestClient import

Frontend (eslint):
- Remove unused imports/variables across 10 files
- Fix explicit any types in client.ts and sessions.ts
- Clean up empty block statements in terminal.tsx

Quality gates: ruff (pass), eslint (pass), tsc --noEmit (pass),
pytest (98 passed, 4 pre-existing failures)

apps/web/src/pages/ssh-keys.tsx

@@ -7,7 +7,7 @@ import { useAsyncData } from "../hooks/use-async-data";
 
 export const SSHKeysPage = () => {
   const navigate = useNavigate();
-  const { data: keys, status, error, reload: loadKeys } = useAsyncData<SSHKey[]>(listSSHKeys, []);
+  const { data: keys, status, reload: loadKeys } = useAsyncData<SSHKey[]>(listSSHKeys, []);
   const [newKeyName, setNewKeyName] = useState("");
   const [generating, setGenerating] = useState(false);
   const [signPayloads, setSignPayloads] = useState<Record<string, string>>({});