feat(db): add timezone column to GetUser query

The GetUser query did not select the timezone column, so the router
helper could not access userDB.Timezone. Added u.timezone to the
SELECT list so the per-user timezone is available in the template
user context.

internal/database/queries/queries.sql

@@ -27,6 +27,7 @@ SELECT
     u.max_devices,
     u.created_at,
     u.updated_at,
+    u.timezone,
     (SELECT COUNT(*) FROM devices WHERE user_id = u.id) as device_count
 FROM users u
 WHERE u.id = $1;