fix: delete all user-related records before removing user to prevent FK constraint error

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

CLAUDE.md

@@ -163,6 +163,13 @@ GitHub Actions with two workflows:
 
 **Docker**: Multi-stage Dockerfile (node:22-slim), exposes port 3000, persists data to `/data` volume.
 
+## Database schema changes
+
+When adding or modifying tables in `src/lib/server/db/schema.ts`:
+
+- **If the table has a foreign key to `users`**: update `deleteUser()` in `src/lib/server/auth.ts` to delete from the new table before the user row is removed. Order matters — delete child rows before parent rows.
+- **If the table has a foreign key to `notes`**: either add `onDelete: 'cascade'` in the schema definition, or add explicit cleanup in the note deletion logic.
+
 ## Testing philosophy: BDD/TDD
 
 Write tests first or alongside features. Tests serve as living documentation of expected behavior.

src/lib/server/auth.ts

@@ -228,6 +228,12 @@ export function getUser(userId: number): User | null {
 
 export async function deleteUser(userId: number): Promise<void> {
 	// Cascade: delete user's data in dependency order
+	sqlite.prepare('DELETE FROM user_preferences WHERE user_id = ?').run(userId);
+	sqlite.prepare('DELETE FROM api_keys WHERE user_id = ?').run(userId);
+	sqlite.prepare('DELETE FROM note_user_state WHERE user_id = ?').run(userId);
+	sqlite
+		.prepare('DELETE FROM note_collaborators WHERE user_id = ? OR added_by = ?')
+		.run(userId, userId);
 	sqlite.prepare('DELETE FROM sync_log WHERE user_id = ?').run(userId);
 	sqlite.prepare('DELETE FROM attachments WHERE user_id = ?').run(userId);
 	sqlite