chore(lint): apply ruff --fix (4443 auto-fixes)

Auto-fixed categories:
- F401: unused imports removed
- I001: import blocks sorted
- W293: trailing whitespace stripped
- UP035: deprecated typing imports replaced
- SIM: simplify suggestions applied
- ARG: unused args prefixed with underscore
- T201: print statements removed
- F841: unused variables removed
- RUF059: unpacked variables prefixed

Remaining ~1500 unfixable errors (C901, B904, N806, E402) require manual work.

Backend smoke tests: 13/13 passed.

backend/src/api/routes/settings.py

@@ -9,28 +9,29 @@
 # @INVARIANT: All settings changes must be persisted via ConfigManager.
 # @PUBLIC_API: router
 
+
 from fastapi import APIRouter, Depends, HTTPException
-from typing import List
 from pydantic import BaseModel
-from ...core.config_models import AppConfig, Environment, GlobalSettings, LoggingConfig
-from ...models.storage import StorageConfig
-from ...dependencies import get_config_manager, has_permission
-from ...core.config_manager import ConfigManager
-from ...core.logger import logger, belief_scope
-from ...core.superset_client import SupersetClient
-from ...services.llm_prompt_templates import normalize_llm_settings
-from ...models.llm import ValidationPolicy
-from ...models.config import AppConfigRecord
-from ...schemas.settings import (
-    ValidationPolicyCreate,
-    ValidationPolicyUpdate,
-    ValidationPolicyResponse,
-    TranslationScheduleItem,
-)
-from ...models.translate import TranslationSchedule, TranslationJob
-from ...core.database import get_db
 from sqlalchemy.orm import Session
 
+from ...core.config_manager import ConfigManager
+from ...core.config_models import AppConfig, Environment, GlobalSettings, LoggingConfig
+from ...core.database import get_db
+from ...core.logger import belief_scope, logger
+from ...core.superset_client import SupersetClient
+from ...dependencies import get_config_manager, has_permission
+from ...models.config import AppConfigRecord
+from ...models.llm import ValidationPolicy
+from ...models.storage import StorageConfig
+from ...models.translate import TranslationJob, TranslationSchedule
+from ...schemas.settings import (
+    TranslationScheduleItem,
+    ValidationPolicyCreate,
+    ValidationPolicyResponse,
+    ValidationPolicyUpdate,
+)
+from ...services.llm_prompt_templates import normalize_llm_settings
+
 
 # #region LoggingConfigResponse [C:1] [TYPE Class] [SEMANTICS logging, config, response]
 # @BRIEF Response model for logging configuration with current task log level.
@@ -179,7 +180,7 @@ async def update_storage_settings(
 # @BRIEF Lists all configured Superset environments.
 # @PRE:     Config manager is available.
 # @POST:    Returns list of environments.
-@router.get("/environments", response_model=List[Environment])
+@router.get("/environments", response_model=list[Environment])
 async def get_environments(
     config_manager: ConfigManager = Depends(get_config_manager),
     _=Depends(has_permission("admin:settings", "READ")),
@@ -375,10 +376,10 @@ async def update_logging_config(
 # #region ConsolidatedSettingsResponse [C:1] [TYPE Class]
 # @BRIEF Response model for consolidated application settings.
 class ConsolidatedSettingsResponse(BaseModel):
-    environments: List[dict]
-    connections: List[dict]
+    environments: list[dict]
+    connections: list[dict]
     llm: dict
-    llm_providers: List[dict]
+    llm_providers: list[dict]
     logging: dict
     storage: dict
     notifications: dict = {}
@@ -410,8 +411,8 @@ async def get_consolidated_settings(
 
         config = config_manager.get_config()
 
-        from ...services.llm_provider import LLMProviderService
         from ...core.database import SessionLocal
+        from ...services.llm_provider import LLMProviderService
 
         db = SessionLocal()
         notifications_payload = {}
@@ -524,7 +525,7 @@ async def update_consolidated_settings(
 
 # #region get_validation_policies [C:2] [TYPE Function]
 # @BRIEF Lists all validation policies.
-@router.get("/automation/policies", response_model=List[ValidationPolicyResponse])
+@router.get("/automation/policies", response_model=list[ValidationPolicyResponse])
 async def get_validation_policies(
     db: Session = Depends(get_db), _=Depends(has_permission("admin:settings", "READ"))
 ):
@@ -603,7 +604,7 @@ async def delete_validation_policy(
 
 # #region get_translation_schedules [C:2] [TYPE Function]
 # @BRIEF Lists all translation schedules joined with translation job names.
-@router.get("/automation/translation-schedules", response_model=List[TranslationScheduleItem])
+@router.get("/automation/translation-schedules", response_model=list[TranslationScheduleItem])
 async def get_translation_schedules(
     db: Session = Depends(get_db),
     _=Depends(has_permission("admin:settings", "READ")),