feat(contracts): Multi-signer e-signature system with PDF overlay

- Add multi-signer contract creation with staff/customer selection
- Add signer-specific signing URLs (/sign/s/{token})
- Add sequential and parallel signing modes
- Fix can_sign check in frontend (use top-level response field)
- Fix required field validation to work for all template types
- Fix PDF overlay generation for HTML templates with generated PDFs
- Add signature pre-fill support in template field editor
- Add signature remember/re-apply feature during signing
- Update PDFOverlayService to read from contract.original_pdf_path

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/vitest.config.ts

@@ -0,0 +1,38 @@
+import { defineConfig } from 'vitest/config';
+import react from '@vitejs/plugin-react';
+import path from 'path';
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    setupFiles: './src/test/setup.ts',
+    css: true,
+    testTimeout: 10000, // 10 seconds per test
+    exclude: [
+      'node_modules/**',
+      'tests/e2e/**',
+      '**/*.spec.ts',
+      '**/*.spec.tsx',
+    ],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      exclude: [
+        'node_modules/',
+        'src/__tests__/',
+        'src/test/',
+        '**/*.d.ts',
+        '**/*.config.*',
+        '**/mockData',
+        '**/*.spec.*',
+      ],
+    },
+  },
+  resolve: {
+    alias: {
+      '@': path.resolve(__dirname, './src'),
+    },
+  },
+});