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/tests/unit/test_git_mount_resolution.py

@@ -1,7 +1,6 @@
 """Unit tests for git mount resolution in tool instances."""
 
 import os
-import tempfile
 from pathlib import Path
 
 import pytest
@@ -11,7 +10,6 @@ from src.api.tool_instances import (
     _expand_glob_source,
     _resolve_single_git_mount,
 )
-from src.services.config_profile_resolver import ResolvedProfile
 
 
 class TestExpandGlobSource: