Replace deprecated datetime.utcnow() with timezone-aware UTC

Use datetime.now(timezone.utc) instead of deprecated utcnow().

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/database/models.py

@@ -1,10 +1,15 @@
 """SQLModel database models for caching PIM data."""
 
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Optional
 from sqlmodel import SQLModel, Field
 
 
+def utc_now() -> datetime:
+    """Return timezone-aware UTC datetime."""
+    return datetime.now(timezone.utc)
+
+
 class CacheMeta(SQLModel, table=True):
     """Generic key-value cache metadata."""
 
@@ -29,7 +34,7 @@ class EmailCache(SQLModel, table=True):
     is_flagged: bool = False
     snippet: Optional[str] = None
     full_data: Optional[str] = Field(default=None, description="JSON blob of full email data")
-    cached_at: datetime = Field(default_factory=datetime.utcnow)
+    cached_at: datetime = Field(default_factory=utc_now)
 
 
 class EventCache(SQLModel, table=True):
@@ -43,7 +48,7 @@ class EventCache(SQLModel, table=True):
     start_time: Optional[datetime] = Field(default=None, index=True)
     end_time: Optional[datetime] = None
     full_data: Optional[str] = Field(default=None, description="JSON blob of full event data")
-    cached_at: datetime = Field(default_factory=datetime.utcnow)
+    cached_at: datetime = Field(default_factory=utc_now)
 
 
 class ContactCache(SQLModel, table=True):
@@ -56,7 +61,7 @@ class ContactCache(SQLModel, table=True):
     display_name: Optional[str] = Field(default=None, index=True)
     primary_email: Optional[str] = None
     full_data: Optional[str] = Field(default=None, description="JSON blob of full contact data")
-    cached_at: datetime = Field(default_factory=datetime.utcnow)
+    cached_at: datetime = Field(default_factory=utc_now)
 
 
 class SyncState(SQLModel, table=True):
@@ -86,7 +91,7 @@ class SeenEmail(SQLModel, table=True):
     from_address: Optional[str] = Field(default=None, description="Sender email for logging")
     subject: Optional[str] = Field(default=None, description="Subject for logging")
     email_date: Optional[datetime] = Field(default=None, description="Email date")
-    seen_at: datetime = Field(default_factory=datetime.utcnow)
+    seen_at: datetime = Field(default_factory=utc_now)
     notification_sent: bool = Field(default=False)
     notification_sent_at: Optional[datetime] = None
     notification_error: Optional[str] = Field(