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/alembic/versions/0014_merge_heads.py

@@ -7,8 +7,6 @@ Create Date: 2026-05-22 21:50:00.000000
 """
 from typing import Sequence, Union
 
-from alembic import op
-import sqlalchemy as sa
 
 # revision identifiers, used by Alembic.
 revision: str = "0014_merge_heads"

apps/api/alembic/versions/0015_single_interface.py

@@ -10,7 +10,6 @@ from typing import Sequence, Union
 from alembic import op
 import sqlalchemy as sa
 from sqlalchemy.dialects import postgresql
-from sqlalchemy import inspect
 
 # revision identifiers, used by Alembic.
 revision: str = "0015_single_interface"

apps/api/alembic/versions/20260527160017_add_pi_agent_tool_type.py

@@ -1,5 +1,3 @@
-import json
-
 """add pi agent tool type
 
 Revision ID: 20260527_160017_add_pi_agent
@@ -7,6 +5,8 @@ Revises: f3d2dc90ba3a
 Create Date: 2026-05-27T16:00:17
 
 """
+
+import json
 from typing import Sequence, Union
 
 from alembic import op

apps/api/alembic/versions/6fc7bfcf199f_merge_remove_is_builtin_and_add_config_.py

@@ -5,8 +5,6 @@ Revises: 2026_05_23_remove_is_builtin, 2026_05_24_add_config_profiles
 Create Date: 2026-05-24 18:00:43.990361
 """
 
-from alembic import op
-import sqlalchemy as sa
 
 
 

apps/api/alembic/versions/f3d2dc90ba3a_merge_single_interface_and_clone_mode.py

@@ -7,8 +7,6 @@ Create Date: 2026-05-24 10:43:14.000000
 """
 from typing import Sequence, Union
 
-from alembic import op
-import sqlalchemy as sa
 
 # revision identifiers, used by Alembic.
 revision: str = "f3d2dc90ba3a"