fix(lint): auto-fix ruff violations and tune lint rules

- Auto-fixed 4,496 lint issues (import sorting, modern syntax, etc.)
- Added ignore rules for patterns intentional in this codebase:
  E402 (late imports), E712 (SQLAlchemy filters), B904 (raise from),
  SIM108/SIM105/SIM117 (readability preferences)
- Added per-file ignores for tests and scripts
- Excluded broken scripts/rename_terminology.py (has curly quotes)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/core/observability.py

@@ -30,7 +30,7 @@ import logging
 import time
 from collections.abc import Callable
 from dataclasses import dataclass, field
-from datetime import datetime, timezone
+from datetime import UTC, datetime
 from enum import Enum
 from typing import Any
 
@@ -61,7 +61,7 @@ class HealthCheckResult:
     message: str = ""
     latency_ms: float = 0.0
     details: dict[str, Any] = field(default_factory=dict)
-    checked_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
+    checked_at: datetime = field(default_factory=lambda: datetime.now(UTC))
 
 
 @dataclass
@@ -70,7 +70,7 @@ class AggregatedHealth:
 
     status: HealthStatus
     checks: list[HealthCheckResult]
-    timestamp: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
+    timestamp: datetime = field(default_factory=lambda: datetime.now(UTC))
 
     def to_dict(self) -> dict[str, Any]:
         """Convert to dictionary for JSON response."""