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/einwilligungen_routes.py

@@ -15,7 +15,7 @@ Endpoints:
 """
 
 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
@@ -131,7 +131,7 @@ async def upsert_catalog(
     if record:
         record.selected_data_point_ids = request.selected_data_point_ids
         record.custom_data_points = request.custom_data_points
-        record.updated_at = datetime.utcnow()
+        record.updated_at = datetime.now(timezone.utc)
     else:
         record = EinwilligungenCatalogDB(
             tenant_id=tenant_id,
@@ -184,7 +184,7 @@ async def upsert_company(
 
     if record:
         record.data = request.data
-        record.updated_at = datetime.utcnow()
+        record.updated_at = datetime.now(timezone.utc)
     else:
         record = EinwilligungenCompanyDB(tenant_id=tenant_id, data=request.data)
         db.add(record)
@@ -233,7 +233,7 @@ async def upsert_cookies(
     if record:
         record.categories = request.categories
         record.config = request.config
-        record.updated_at = datetime.utcnow()
+        record.updated_at = datetime.now(timezone.utc)
     else:
         record = EinwilligungenCookiesDB(
             tenant_id=tenant_id,
@@ -374,7 +374,7 @@ async def create_consent(
         user_id=request.user_id,
         data_point_id=request.data_point_id,
         granted=request.granted,
-        granted_at=datetime.utcnow(),
+        granted_at=datetime.now(timezone.utc),
         consent_version=request.consent_version,
         source=request.source,
         ip_address=request.ip_address,
@@ -443,7 +443,7 @@ async def revoke_consent(
     if consent.revoked_at:
         raise HTTPException(status_code=400, detail="Consent is already revoked")
 
-    consent.revoked_at = datetime.utcnow()
+    consent.revoked_at = datetime.now(timezone.utc)
     _record_history(db, consent, 'revoked')
     db.commit()
     db.refresh(consent)