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/email_template_routes.py

@@ -6,7 +6,7 @@ Inklusive Versionierung, Approval-Workflow, Vorschau und Send-Logging.
 """
 
 import uuid
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Optional, Dict
 
 from fastapi import APIRouter, Depends, HTTPException, Query, Header
@@ -271,7 +271,7 @@ async def update_settings(
         if val is not None:
             setattr(settings, field, val)
 
-    settings.updated_at = datetime.utcnow()
+    settings.updated_at = datetime.now(timezone.utc)
     db.commit()
     db.refresh(settings)
 
@@ -638,7 +638,7 @@ async def submit_version(
         raise HTTPException(status_code=400, detail="Only draft versions can be submitted")
 
     v.status = "review"
-    v.submitted_at = datetime.utcnow()
+    v.submitted_at = datetime.now(timezone.utc)
     v.submitted_by = "admin"
     db.commit()
     db.refresh(v)
@@ -730,7 +730,7 @@ async def publish_version(
     if v.status not in ("approved", "review", "draft"):
         raise HTTPException(status_code=400, detail="Version cannot be published")
 
-    now = datetime.utcnow()
+    now = datetime.now(timezone.utc)
     v.status = "published"
     v.published_at = now
     v.published_by = "admin"