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/models/translate.py

@@ -3,14 +3,11 @@
 # @LAYER: Domain
 # @RELATION INHERITS_FROM -> MappingModels:Base
 
-from sqlalchemy import (
-    Column, String, Boolean, DateTime, JSON, Text,
-    ForeignKey, Integer, UniqueConstraint, Index
-)
-from sqlalchemy.dialects.postgresql import JSON as PG_JSON
-from datetime import datetime, timezone
 import uuid
-import hashlib
+from datetime import UTC, datetime
+
+from sqlalchemy import JSON, Boolean, Column, DateTime, ForeignKey, Index, Integer, String, Text, UniqueConstraint
+
 from .mapping import Base
 
 
@@ -57,8 +54,8 @@ class TranslationJob(Base):
     target_database_id = Column(String, nullable=True, comment="Superset database ID for SQL Lab insert target")
 
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
+    updated_at = Column(DateTime, default=lambda: datetime.now(UTC), onupdate=lambda: datetime.now(UTC))
 # #endregion TranslationJob
 
 
@@ -86,7 +83,7 @@ class TranslationRun(Base):
     config_hash = Column(String, nullable=True, comment="Hash of translation configuration state")
     dict_snapshot_hash = Column(String, nullable=True, comment="Hash of dictionary state at run time")
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 # #endregion TranslationRun
 
 
@@ -104,7 +101,7 @@ class TranslationBatch(Base):
     failed_records = Column(Integer, default=0)
     started_at = Column(DateTime, nullable=True)
     completed_at = Column(DateTime, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 # #endregion TranslationBatch
 
 
@@ -127,7 +124,7 @@ class TranslationRecord(Base):
     token_count_input = Column(Integer, nullable=True)
     token_count_output = Column(Integer, nullable=True)
     translation_duration_ms = Column(Integer, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 
     __table_args__ = (
         Index("ix_translation_records_run_status", "run_id", "status"),
@@ -146,7 +143,7 @@ class TranslationEvent(Base):
     event_type = Column(String, nullable=False)  # JOB_CREATED, JOB_STARTED, JOB_COMPLETED, JOB_FAILED, etc.
     event_data = Column(JSON, nullable=True)
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 # #endregion TranslationEvent
 
 
@@ -160,7 +157,7 @@ class TranslationPreviewSession(Base):
     run_id = Column(String, ForeignKey("translation_runs.id"), nullable=True)
     status = Column(String, nullable=False, default="ACTIVE")  # ACTIVE, APPLIED, DISCARDED, EXPIRED
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
     expires_at = Column(DateTime, nullable=True)
 # #endregion TranslationPreviewSession
 
@@ -180,7 +177,7 @@ class TranslationPreviewRecord(Base):
     source_data = Column(JSON, nullable=True, comment="Original source row key columns for upsert matching")
     status = Column(String, nullable=False, default="PENDING")  # PENDING, APPROVED, REJECTED
     feedback = Column(Text, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 # #endregion TranslationPreviewRecord
 
 
@@ -196,8 +193,8 @@ class TerminologyDictionary(Base):
     target_dialect = Column(String, nullable=False)
     is_active = Column(Boolean, default=True)
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
+    updated_at = Column(DateTime, default=lambda: datetime.now(UTC), onupdate=lambda: datetime.now(UTC))
 # #endregion TerminologyDictionary
 
 
@@ -215,8 +212,8 @@ class DictionaryEntry(Base):
     origin_run_id = Column(String, nullable=True, comment="Run ID from which this correction originated")
     origin_row_key = Column(String, nullable=True, comment="Row key within the run that triggered this correction")
     origin_user_id = Column(String, nullable=True, comment="User who submitted the correction")
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
+    updated_at = Column(DateTime, default=lambda: datetime.now(UTC), onupdate=lambda: datetime.now(UTC))
 
     __table_args__ = (
         UniqueConstraint(
@@ -241,8 +238,8 @@ class TranslationSchedule(Base):
     next_run_at = Column(DateTime, nullable=True)
     execution_mode = Column(String, nullable=False, default="full", comment="full, new_key_only")
     created_by = Column(String, nullable=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
-    updated_at = Column(DateTime, default=lambda: datetime.now(timezone.utc), onupdate=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
+    updated_at = Column(DateTime, default=lambda: datetime.now(UTC), onupdate=lambda: datetime.now(UTC))
 # #endregion TranslationSchedule
 
 
@@ -254,7 +251,7 @@ class TranslationJobDictionary(Base):
     id = Column(String, primary_key=True, default=generate_uuid)
     job_id = Column(String, ForeignKey("translation_jobs.id"), nullable=False, index=True)
     dictionary_id = Column(String, ForeignKey("terminology_dictionaries.id"), nullable=False, index=True)
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 
     __table_args__ = (
         UniqueConstraint(
@@ -287,8 +284,8 @@ class MetricSnapshot(Base):
     p50_duration_ms = Column(Integer, nullable=True)
     p95_duration_ms = Column(Integer, nullable=True)
     p99_duration_ms = Column(Integer, nullable=True)
-    snapshot_date = Column(DateTime, nullable=False, default=lambda: datetime.now(timezone.utc))
-    created_at = Column(DateTime, default=lambda: datetime.now(timezone.utc))
+    snapshot_date = Column(DateTime, nullable=False, default=lambda: datetime.now(UTC))
+    created_at = Column(DateTime, default=lambda: datetime.now(UTC))
 
     __table_args__ = (
         Index("ix_metric_snapshots_job_date", "job_id", "snapshot_date"),