fix: separate client and server utilities to fix build error

Split lib/utils.ts into:
- lib/utils.ts: Client-safe utilities only (no Node.js imports)
- lib/project-utils.ts: Server-only utilities with Node.js imports

This fixes the Next.js build error where client components were importing
modules that contained Node.js dependencies (fs, path).

All tests pass and build succeeds.

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

app/api/__tests__/projects.test.ts

@@ -6,7 +6,7 @@ import { GET } from '../projects/route';
 import { getProjects } from '@/lib/fs-utils';
 
 jest.mock('@/lib/fs-utils');
-jest.mock('@/lib/utils', () => ({
+jest.mock('@/lib/project-utils', () => ({
   getProjectDisplayName: jest.fn((name) => name === 'FT' ? '外放构建' : name),
 }));