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/package.json

@@ -13,6 +13,7 @@
     "@stripe/stripe-js": "^8.5.3",
     "@tanstack/react-query": "^5.90.10",
     "@types/react-grid-layout": "^1.3.6",
+    "@types/react-signature-canvas": "^1.0.7",
     "@types/react-syntax-highlighter": "^15.5.13",
     "axios": "^1.13.2",
     "date-fns": "^4.1.0",
@@ -21,6 +22,7 @@
     "i18next-browser-languagedetector": "^8.2.0",
     "i18next-http-backend": "^3.0.2",
     "lucide-react": "^0.554.0",
+    "pdfjs-dist": "^5.4.449",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-grid-layout": "^1.5.2",
@@ -28,6 +30,7 @@
     "react-i18next": "^16.3.5",
     "react-phone-number-input": "^3.4.14",
     "react-router-dom": "^7.9.6",
+    "react-signature-canvas": "^1.1.0-alpha.2",
     "react-syntax-highlighter": "^16.1.0",
     "recharts": "^3.5.0"
   },
@@ -35,27 +38,37 @@
     "@eslint/js": "^9.39.1",
     "@playwright/test": "^1.48.0",
     "@tailwindcss/postcss": "^4.1.17",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.0",
+    "@testing-library/user-event": "^14.6.1",
     "@types/node": "^24.10.1",
     "@types/react": "^19.2.6",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^5.1.1",
+    "@vitest/coverage-v8": "^4.0.15",
     "autoprefixer": "^10.4.22",
     "eslint": "^9.39.1",
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.4.24",
     "globals": "^16.5.0",
+    "jsdom": "^27.2.0",
+    "msw": "^2.12.4",
     "postcss": "^8.5.6",
     "tailwindcss": "^4.1.17",
     "typescript": "^5.9.3",
-    "vite": "^7.2.4"
+    "vite": "^7.2.4",
+    "vitest": "^4.0.15"
   },
   "scripts": {
     "dev": "vite",
     "build": "vite build",
     "lint": "eslint .",
     "preview": "vite preview",
-    "test": "playwright test",
-    "test:ui": "playwright test --ui",
-    "test:headed": "playwright test --headed"
+    "test": "vitest",
+    "test:ui": "vitest --ui",
+    "test:coverage": "vitest --coverage",
+    "test:e2e": "playwright test",
+    "test:e2e:ui": "playwright test --ui",
+    "test:e2e:headed": "playwright test --headed"
   }
 }