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/tests/core/test_migration_engine.py

@@ -4,24 +4,21 @@
 # @LAYER:     Domain
 # @RELATION: VERIFIES -> [src.core.migration_engine:Module]
 #
-import pytest
-import tempfile
 import json
-import yaml
-import zipfile
-import sys
 import os
+import sys
+import tempfile
+import zipfile
 from pathlib import Path
-from unittest.mock import MagicMock
+
+import pytest
+import yaml
 
 backend_dir = str(Path(__file__).parent.parent.parent.resolve())
 if backend_dir not in sys.path:
     sys.path.insert(0, backend_dir)
 
 from src.core.migration_engine import MigrationEngine
-from src.core.mapping_service import IdMappingService
-from src.models.mapping import ResourceType
-
 
 # --- Fixtures ---
 
@@ -80,7 +77,7 @@ def test_patch_dashboard_metadata_replaces_chart_ids():
 
         engine._patch_dashboard_metadata(fp, "target-env", source_map)
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             result = json.loads(data["json_metadata"])
             assert (
@@ -107,7 +104,7 @@ def test_patch_dashboard_metadata_replaces_dataset_ids():
 
         engine._patch_dashboard_metadata(fp, "target-env", source_map)
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             result = json.loads(data["json_metadata"])
             assert (
@@ -134,7 +131,7 @@ def test_patch_dashboard_metadata_skips_when_no_metadata():
 
         engine._patch_dashboard_metadata(fp, "target-env", {})
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             assert "json_metadata" not in data
 
@@ -162,7 +159,7 @@ def test_patch_dashboard_metadata_handles_missing_targets():
 
         engine._patch_dashboard_metadata(fp, "target-env", source_map)
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             result = json.loads(data["json_metadata"])
             targets = result["native_filter_configuration"][0]["targets"]
@@ -219,7 +216,7 @@ def test_transform_yaml_replaces_database_uuid():
 
         engine._transform_yaml(fp, {"source-uuid-abc": "target-uuid-xyz"})
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             assert data["database_uuid"] == "target-uuid-xyz"
             assert data["table_name"] == "my_table"
@@ -243,7 +240,7 @@ def test_transform_yaml_ignores_unmapped_uuid():
 
         engine._transform_yaml(fp, {"other-uuid": "replacement"})
 
-        with open(fp, "r") as f:
+        with open(fp) as f:
             data = yaml.safe_load(f)
             assert data["database_uuid"] == "unknown-uuid"
 
@@ -317,12 +314,12 @@ def test_transform_zip_end_to_end():
             out_path = Path(out_dir)
 
             # Verify dataset transformation
-            with open(out_path / "datasets" / "ds.yaml", "r") as f:
+            with open(out_path / "datasets" / "ds.yaml") as f:
                 ds_data = yaml.safe_load(f)
                 assert ds_data["database_uuid"] == "target-db-uuid"
 
             # Verify dashboard patching
-            with open(out_path / "dashboards" / "db.yaml", "r") as f:
+            with open(out_path / "dashboards" / "db.yaml") as f:
                 db_data = yaml.safe_load(f)
                 meta = json.loads(db_data["json_metadata"])
                 assert (