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/profile.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from "react";
 
 import { getProfile, updateProfile, uploadAvatar } from "../api/profile";
-import { EmptyState, ErrorState, LoadingState } from "../components/data-states";
+import { ErrorState, LoadingState } from "../components/data-states";
 import { Icon } from "../components/icon";
 import { useAuth } from "../state/auth";
 import { useAsyncData } from "../hooks/use-async-data";