fix: resolve all 153 ruff lint errors for CI

Auto-fixed 138 unused imports and f-string issues. Manually fixed:
ambiguous variable names (l→layer), availability-check imports using
importlib.util.find_spec, unused Color import, ImagePool forward ref
via TYPE_CHECKING, multi-statement semicolons, and E402 suppression.

server/tests/e2e/test_auth_flow.py

@@ -7,9 +7,7 @@ Uses the `client` fixture (which has the correct auth header set), and
 helpers to make unauthenticated requests by temporarily removing the header.
 """
 
-import pytest
 
-from tests.e2e.conftest import API_KEY
 
 
 def _unauth_get(client, url):

server/tests/e2e/test_backup_flow.py

@@ -6,7 +6,6 @@ Tests creating entities, backing up, deleting, then restoring from backup.
 import io
 import json
 
-import pytest
 
 
 class TestBackupRestoreFlow:

server/tests/e2e/test_color_strip_flow.py

@@ -3,7 +3,6 @@
 Tests creating, listing, updating, cloning, and deleting color strip sources.
 """
 
-import pytest
 
 
 class TestColorStripSourceLifecycle:

server/tests/e2e/test_device_flow.py

@@ -4,7 +4,6 @@ Tests the complete device lifecycle through the API:
 create -> get -> update -> brightness -> power -> delete -> verify gone.
 """
 
-import pytest
 
 
 class TestDeviceLifecycle:

server/tests/e2e/test_target_flow.py

@@ -4,7 +4,6 @@ Tests target CRUD with a dependency on a device:
 create device -> create target -> list -> update -> delete target -> cleanup device.
 """
 
-import pytest
 
 
 class TestOutputTargetLifecycle: