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/tests/test_auto_risk_updater.py

@@ -4,7 +4,7 @@ Tests for the AutoRiskUpdater Service.
 Sprint 6: CI/CD Evidence Collection & Automatic Risk Updates (2026-01-18)
 """
 
-from datetime import datetime
+from datetime import datetime, timezone
 from unittest.mock import MagicMock
 
 from ..services.auto_risk_updater import (
@@ -188,7 +188,7 @@ class TestGenerateAlerts:
         scan_result = ScanResult(
             scan_type=ScanType.DEPENDENCY,
             tool="Trivy",
-            timestamp=datetime.utcnow(),
+            timestamp=datetime.now(timezone.utc),
             commit_sha="abc123",
             branch="main",
             control_id="SDLC-002",
@@ -209,7 +209,7 @@ class TestGenerateAlerts:
         scan_result = ScanResult(
             scan_type=ScanType.SAST,
             tool="Semgrep",
-            timestamp=datetime.utcnow(),
+            timestamp=datetime.now(timezone.utc),
             commit_sha="def456",
             branch="main",
             control_id="SDLC-001",
@@ -228,7 +228,7 @@ class TestGenerateAlerts:
         scan_result = ScanResult(
             scan_type=ScanType.CONTAINER,
             tool="Trivy",
-            timestamp=datetime.utcnow(),
+            timestamp=datetime.now(timezone.utc),
             commit_sha="ghi789",
             branch="main",
             control_id="SDLC-006",
@@ -247,7 +247,7 @@ class TestGenerateAlerts:
         scan_result = ScanResult(
             scan_type=ScanType.SAST,
             tool="Semgrep",
-            timestamp=datetime.utcnow(),
+            timestamp=datetime.now(timezone.utc),
             commit_sha="jkl012",
             branch="main",
             control_id="SDLC-001",
@@ -369,7 +369,7 @@ class TestScanResult:
         result = ScanResult(
             scan_type=ScanType.DEPENDENCY,
             tool="Trivy",
-            timestamp=datetime.utcnow(),
+            timestamp=datetime.now(timezone.utc),
             commit_sha="xyz789",
             branch="develop",
             control_id="SDLC-002",