fix: resolve pylint and type-checking issues

- Fix return type annotation in SetupRedirectMiddleware.dispatch() to use Response instead of RedirectResponse
- Replace broad 'except Exception' with specific exception types (FileNotFoundError, ValueError, OSError, etc.)
- Rename AppConfig.validate() to validate_config() to avoid shadowing BaseModel.validate()
- Fix ValidationResult.errors field to use List[str] with default_factory
- Add pylint disable comments for intentional broad exception catches during shutdown
- Rename lifespan parameter to _application to indicate unused variable
- Update all callers to use new validate_config() method name

tests/unit/test_config_models.py

@@ -44,12 +44,12 @@ def test_appconfig_and_config_update_apply_to():
 def test_backup_and_validation():
     cfg = AppConfig()
     # default backups disabled -> valid
-    res: ValidationResult = cfg.validate()
+    res: ValidationResult = cfg.validate_config()
     assert res.valid is True
 
     # enable backups but leave path empty -> invalid
     cfg.backup.enabled = True
     cfg.backup.path = ""
-    res2 = cfg.validate()
+    res2 = cfg.validate_config()
     assert res2.valid is False
     assert any("backup.path" in e for e in res2.errors)