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/api/src/main.py

@@ -1,4 +1,3 @@
-import json
 import logging
 import os
 
@@ -7,7 +6,6 @@ from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
-from sqlalchemy import text
 
 from src.api.auth import router as auth_router
 from src.api.dashboard import router as dashboard_router