fix: unique constraint check crash and copilot table initial rows

- Fix TypeError in updateColumnConstraints: db.execute() returns a
  plain array with postgres-js, not { rows: [...] }. The .rows.length
  access always crashed, making "Set unique" completely broken.

- Add initialRowCount: 20 to copilot table creation so tables created
  via chat have the same empty rows as tables created from the UI.

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

Author: waleedlatif1

apps/sim/lib/copilot/tools/server/table/user-table.ts

@@ -229,6 +229,7 @@ export const userTableServerTool: BaseServerTool<UserTableArgs, UserTableResult>
               schema: args.schema,
               workspaceId,
               userId: context.userId,
+              initialRowCount: 20,
             },
             requestId
           )