Fix AsyncSession API: use execute() instead of exec()

SQLAlchemy's AsyncSession uses execute() + scalars(), not SQLModel's exec().

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

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

src/services/email_monitor.py

@@ -294,10 +294,10 @@ class EmailMonitor:
         """Seed the seen_emails table with existing emails on first run."""
         async with get_session() as session:
             # Check if this mailbox has been seeded
-            result = await session.exec(
+            result = await session.execute(
                 select(CacheMeta).where(CacheMeta.key == f"seeded_{mailbox}")
             )
-            if result.first():
+            if result.scalars().first():
                 logger.debug(f"Mailbox {mailbox} already seeded")
                 return
 
@@ -334,12 +334,12 @@ class EmailMonitor:
     async def _is_email_seen(self, email_uid: str, mailbox: str) -> bool:
         """Check if email has already been processed."""
         async with get_session() as session:
-            result = await session.exec(
+            result = await session.execute(
                 select(SeenEmail).where(
                     SeenEmail.email_uid == email_uid, SeenEmail.mailbox == mailbox
                 )
             )
-            return result.first() is not None
+            return result.scalars().first() is not None
 
     async def _mark_as_seen(
         self, email: EmailSummary, mailbox: str, notification_sent: bool = False
@@ -367,12 +367,12 @@ class EmailMonitor:
     ):
         """Update the notification status for a seen email."""
         async with get_session() as session:
-            result = await session.exec(
+            result = await session.execute(
                 select(SeenEmail).where(
                     SeenEmail.email_uid == email_uid, SeenEmail.mailbox == mailbox
                 )
             )
-            seen = result.first()
+            seen = result.scalars().first()
             if seen:
                 seen.notification_sent = success
                 seen.notification_sent_at = datetime.utcnow() if success else None