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/services/audit_pdf_generator.py

@@ -16,7 +16,7 @@ Uses reportlab for PDF generation (lightweight, no external dependencies).
 
 import io
 import logging
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Dict, List, Any, Optional, Tuple
 
 from sqlalchemy.orm import Session
@@ -255,7 +255,7 @@ class AuditPDFGenerator:
         doc.build(story)
 
         # Generate filename
-        date_str = datetime.utcnow().strftime('%Y%m%d')
+        date_str = datetime.now(timezone.utc).strftime('%Y%m%d')
         filename = f"audit_report_{session.name.replace(' ', '_')}_{date_str}.pdf"
 
         return buffer.getvalue(), filename
@@ -429,7 +429,7 @@ class AuditPDFGenerator:
         story.append(Spacer(1, 30*mm))
         gen_label = 'Generiert am' if language == 'de' else 'Generated on'
         story.append(Paragraph(
-            f"{gen_label}: {datetime.utcnow().strftime('%d.%m.%Y %H:%M')} UTC",
+            f"{gen_label}: {datetime.now(timezone.utc).strftime('%d.%m.%Y %H:%M')} UTC",
             self.styles['Footer']
         ))