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_dsfa_routes.py

@@ -10,7 +10,7 @@ import pytest
 import uuid
 import os
 import sys
-from datetime import datetime
+from datetime import datetime, timezone
 from unittest.mock import MagicMock
 
 from fastapi import FastAPI
@@ -51,7 +51,7 @@ _RawSessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 @event.listens_for(engine, "connect")
 def _register_sqlite_functions(dbapi_conn, connection_record):
     """Register PostgreSQL-compatible functions for SQLite."""
-    dbapi_conn.create_function("NOW", 0, lambda: datetime.utcnow().isoformat())
+    dbapi_conn.create_function("NOW", 0, lambda: datetime.now(timezone.utc).isoformat())
 
 TENANT_ID = "default"