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/migration.py

@@ -21,16 +21,18 @@
 # @TEST_EDGE: [external_fail] ->[HTTP_500]
 # @TEST_INVARIANT: [EnvironmentValidationBeforeAction] -> VERIFIED_BY: [invalid_environment, valid_execution]
 
+from typing import Any, cast
+
 from fastapi import APIRouter, Depends, HTTPException, Query
-from typing import List, Dict, Any, Optional, cast
 from sqlalchemy.orm import Session
-from ...dependencies import get_config_manager, get_task_manager, has_permission
+
 from ...core.database import get_db
-from ...models.dashboard import DashboardMetadata, DashboardSelection
-from ...core.superset_client import SupersetClient
-from ...core.logger import logger, belief_scope
-from ...core.migration.dry_run_orchestrator import MigrationDryRunService
+from ...core.logger import belief_scope, logger
 from ...core.mapping_service import IdMappingService
+from ...core.migration.dry_run_orchestrator import MigrationDryRunService
+from ...core.superset_client import SupersetClient
+from ...dependencies import get_config_manager, get_task_manager, has_permission
+from ...models.dashboard import DashboardMetadata, DashboardSelection
 from ...models.mapping import ResourceMapping
 
 logger = cast(Any, logger)
@@ -45,7 +47,7 @@ router = APIRouter(prefix="/api", tags=["migration"])
 # @SIDE_EFFECT: Reads environment configuration and performs remote Superset metadata retrieval over network.
 # @DATA_CONTRACT: Input[str env_id] -> Output[List[DashboardMetadata]]
 # @RELATION CALLS -> [SupersetClient.get_dashboards_summary]
-@router.get("/environments/{env_id}/dashboards", response_model=List[DashboardMetadata])
+@router.get("/environments/{env_id}/dashboards", response_model=list[DashboardMetadata])
 async def get_dashboards(
     env_id: str,
     config_manager=Depends(get_config_manager),
@@ -125,7 +127,7 @@ async def execute_migration(
         except Exception as e:
             logger.explore(f"Task creation failed: {e}")
             raise HTTPException(
-                status_code=500, detail=f"Failed to create migration task: {str(e)}"
+                status_code=500, detail=f"Failed to create migration task: {e!s}"
             )
 
 
@@ -141,7 +143,7 @@ async def execute_migration(
 # @RELATION DEPENDS_ON -> [DashboardSelection]
 # @RELATION DEPENDS_ON -> [MigrationDryRunService]
 # @INVARIANT: Dry-run flow remains read-only and rejects identical source/target environments before service execution.
-@router.post("/migration/dry-run", response_model=Dict[str, Any])
+@router.post("/migration/dry-run", response_model=dict[str, Any])
 async def dry_run_migration(
     selection: DashboardSelection,
     config_manager=Depends(get_config_manager),
@@ -205,7 +207,7 @@ async def dry_run_migration(
 # @SIDE_EFFECT: Reads configuration from config manager.
 # @DATA_CONTRACT: Input[None] -> Output[Dict[str, str]]
 # @RELATION DEPENDS_ON -> [AppDependencies]
-@router.get("/migration/settings", response_model=Dict[str, str])
+@router.get("/migration/settings", response_model=dict[str, str])
 async def get_migration_settings(
     config_manager=Depends(get_config_manager),
     _=Depends(has_permission("plugin:migration", "READ")),
@@ -226,9 +228,9 @@ async def get_migration_settings(
 # @SIDE_EFFECT: Mutates configuration and writes persisted config through config manager.
 # @DATA_CONTRACT: Input[Dict[str, str]] -> Output[Dict[str, str]]
 # @RELATION DEPENDS_ON -> [AppDependencies]
-@router.put("/migration/settings", response_model=Dict[str, str])
+@router.put("/migration/settings", response_model=dict[str, str])
 async def update_migration_settings(
-    payload: Dict[str, str],
+    payload: dict[str, str],
     config_manager=Depends(get_config_manager),
     _=Depends(has_permission("plugin:migration", "WRITE")),
 ):
@@ -257,13 +259,13 @@ async def update_migration_settings(
 # @SIDE_EFFECT: Executes database read queries against ResourceMapping table.
 # @DATA_CONTRACT: Input[QueryParams] -> Output[Dict[str, Any]]
 # @RELATION DEPENDS_ON -> [ResourceMapping]
-@router.get("/migration/mappings-data", response_model=Dict[str, Any])
+@router.get("/migration/mappings-data", response_model=dict[str, Any])
 async def get_resource_mappings(
     skip: int = Query(0, ge=0),
     limit: int = Query(50, ge=1, le=500),
-    search: Optional[str] = Query(None, description="Search by resource name or UUID"),
-    env_id: Optional[str] = Query(None, description="Filter by environment ID"),
-    resource_type: Optional[str] = Query(None, description="Filter by resource type"),
+    search: str | None = Query(None, description="Search by resource name or UUID"),
+    env_id: str | None = Query(None, description="Filter by environment ID"),
+    resource_type: str | None = Query(None, description="Filter by resource type"),
     db: Session = Depends(get_db),
     _=Depends(has_permission("plugin:migration", "READ")),
 ):
@@ -330,7 +332,7 @@ async def get_resource_mappings(
 # @DATA_CONTRACT: Input[None] -> Output[Dict[str, Any]]
 # @RELATION DEPENDS_ON -> [IdMappingService]
 # @RELATION CALLS -> [sync_environment]
-@router.post("/migration/sync-now", response_model=Dict[str, Any])
+@router.post("/migration/sync-now", response_model=dict[str, Any])
 async def trigger_sync_now(
     config_manager=Depends(get_config_manager),
     db: Session = Depends(get_db),