chore(backend): deprecation sweep — Pydantic V1 -> V2, utcnow -> tz-aware

Two low-risk Pydantic V1 idioms that will be hard errors in V3:
  - Query(regex=...) -> Query(pattern=...) (audit_routes, control_generator_routes)
  - class Config: from_attributes=True -> model_config = ConfigDict(...)
    in source_policy_router.py (schemas.py is intentionally skipped — it is
    the Phase 1 schema-split target and the ConfigDict conversion is most
    efficient to do during that split).

Naive -> aware datetime sweep across 47 files:
  - datetime.utcnow() -> datetime.now(timezone.utc)
  - default=datetime.utcnow -> default=lambda: datetime.now(timezone.utc)
  - onupdate=datetime.utcnow -> onupdate=lambda: datetime.now(timezone.utc)

All SQLAlchemy DateTime columns in the project already declare
timezone=True, so the DB schema expects aware datetimes. Before this
commit, the in-Python side was generating naive values and the driver
was silently coercing them. This is a latent-bug fix, not a behavior
change at the DB boundary.

Verified:
  - 173/173 pytest compliance/tests/ pass (same as baseline)
  - tests/contracts/test_openapi_baseline.py passes (360 paths,
    484 operations unchanged)
  - DeprecationWarning count dropped from 158 -> 35

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/tests/test_legal_document_routes_extended.py

@@ -5,7 +5,7 @@ Tests for Legal Document extended routes (User Consents, Audit Log, Cookie Categ
 import uuid
 import os
 import sys
-from datetime import datetime
+from datetime import datetime, timezone
 
 import pytest
 from fastapi import FastAPI
@@ -103,7 +103,7 @@ def _publish_version(version_id):
     v = db.query(LegalDocumentVersionDB).filter(LegalDocumentVersionDB.id == vid).first()
     v.status = "published"
     v.approved_by = "admin"
-    v.approved_at = datetime.utcnow()
+    v.approved_at = datetime.now(timezone.utc)
     db.commit()
     db.refresh(v)
     result = {"id": str(v.id), "status": v.status}