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/compliance/api/legal_document_routes.py

@@ -6,7 +6,7 @@ Extended with: Public endpoints, User Consents, Consent Audit Log, Cookie Catego
 
 import uuid as uuid_mod
 import logging
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Optional, List, Any, Dict
 
 from fastapi import APIRouter, Depends, HTTPException, Query, Header, UploadFile, File
@@ -285,7 +285,7 @@ async def update_version(
 
     for field, value in request.dict(exclude_none=True).items():
         setattr(version, field, value)
-    version.updated_at = datetime.utcnow()
+    version.updated_at = datetime.now(timezone.utc)
 
     db.commit()
     db.refresh(version)
@@ -346,7 +346,7 @@ def _transition(
         )
 
     version.status = to_status
-    version.updated_at = datetime.utcnow()
+    version.updated_at = datetime.now(timezone.utc)
     if extra_updates:
         for k, v in extra_updates.items():
             setattr(version, k, v)
@@ -378,7 +378,7 @@ async def approve_version(
     return _transition(
         db, version_id, ['review'], 'approved', 'approved',
         request.approver, request.comment,
-        extra_updates={'approved_by': request.approver, 'approved_at': datetime.utcnow()}
+        extra_updates={'approved_by': request.approver, 'approved_at': datetime.now(timezone.utc)}
     )
 
 
@@ -728,7 +728,7 @@ async def withdraw_consent(
     if consent.withdrawn_at:
         raise HTTPException(status_code=400, detail="Consent already withdrawn")
 
-    consent.withdrawn_at = datetime.utcnow()
+    consent.withdrawn_at = datetime.now(timezone.utc)
     consent.consented = False
 
     _log_consent_audit(
@@ -903,7 +903,7 @@ async def update_cookie_category(
         if val is not None:
             setattr(cat, field, val)
 
-    cat.updated_at = datetime.utcnow()
+    cat.updated_at = datetime.now(timezone.utc)
     db.commit()
     db.refresh(cat)
     return _cookie_cat_to_dict(cat)