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/dashboard_routes.py

@@ -10,7 +10,7 @@ Endpoints:
 """
 
 import logging
-from datetime import datetime, timedelta
+from datetime import datetime, timedelta, timezone
 from calendar import month_abbr
 from typing import Optional
 
@@ -167,7 +167,7 @@ async def get_executive_dashboard(db: Session = Depends(get_db)):
     # Trend data — only show current score, no simulated history
     trend_data = []
     if total > 0:
-        now = datetime.utcnow()
+        now = datetime.now(timezone.utc)
         trend_data.append(TrendDataPoint(
             date=now.strftime("%Y-%m-%d"),
             score=round(score, 1),
@@ -204,7 +204,7 @@ async def get_executive_dashboard(db: Session = Depends(get_db)):
     # Get upcoming deadlines
     controls = ctrl_repo.get_all()
     upcoming_deadlines = []
-    today = datetime.utcnow().date()
+    today = datetime.now(timezone.utc).date()
 
     for ctrl in controls:
         if ctrl.next_review_at:
@@ -280,7 +280,7 @@ async def get_executive_dashboard(db: Session = Depends(get_db)):
         top_risks=top_risks,
         upcoming_deadlines=upcoming_deadlines,
         team_workload=team_workload,
-        last_updated=datetime.utcnow().isoformat(),
+        last_updated=datetime.now(timezone.utc).isoformat(),
     )
 
 
@@ -305,7 +305,7 @@ async def get_compliance_trend(
     # Trend data — only current score, no simulated history
     trend_data = []
     if total > 0:
-        now = datetime.utcnow()
+        now = datetime.now(timezone.utc)
         trend_data.append({
             "date": now.strftime("%Y-%m-%d"),
             "score": round(current_score, 1),
@@ -318,7 +318,7 @@ async def get_compliance_trend(
         "current_score": round(current_score, 1),
         "trend": trend_data,
         "period_months": months,
-        "generated_at": datetime.utcnow().isoformat(),
+        "generated_at": datetime.now(timezone.utc).isoformat(),
     }