style: apply safe ruff auto-fixes and exempt startup late imports

Run `ruff check app tests scripts --fix` with the configured rule set
(E4/E7/E9/F/I): import sorting (I001), f-strings without placeholders
(F541), lambda/variable/unused-import cleanups that ruff marks safe.
Nine files whose only ruff debt sits next to pre-existing pylint
import-resolution errors (lazy exports, sys.path script imports) or
whose "unused" imports are reached through attribute access by tests are
left untouched so the changed-file pylint gate and the benchmark tests
stay green; their diagnostics remain in the baseline.

app/startup/lifecycle/__init__.py and app/main.py import business
modules after cache composition, import-path and stdio setup on purpose
(the source comments document the contract), so declare E402
per-file-ignores for them instead of adding per-line noqa.

Ruff ratchet watermark drops from 498 to 100; sync the baseline fixture
and the optimization checklist figure.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/test_testing_bootstrap_plugin_namespace.py

@@ -1,8 +1,8 @@
 """验证插件仓测试引导复现生产运行时的插件导入命名空间。"""
 
+import sys
 from importlib import import_module
 from pathlib import Path
-import sys
 
 import pytest