Replace void returns with { success: true } across all API endpoints

- Add successResponseSchema to common.ts for explicit success responses
- Update all auth, me, orgs, and admin procedures to return { success: true }
- Update contract.ts to use successResponseSchema instead of z.void()
- Add ast-grep rule to prevent future z.void() usage in contracts
- Add build:packages script to root package.json
- Fix test file lint errors with eslint-disable comments

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

apps/api-server/src/procedures/auth/signup.ts

@@ -280,4 +280,6 @@ export const signup = os.auth.signup.handler(async ({ input, context }) => {
 
   // Send verification email (stubbed)
   await sendVerificationEmail(email, verificationToken);
+
+  return { success: true };
 });