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/SETUP_TESTING.md

@@ -0,0 +1,188 @@
+# Setup Testing for useTenantExists Hook
+
+This guide will help you set up and run the comprehensive tests for the `useTenantExists` hook.
+
+## Quick Setup
+
+### 1. Install Testing Dependencies
+
+Run this command from the frontend directory:
+
+```bash
+cd /home/poduck/Desktop/smoothschedule2/frontend
+
+npm install -D vitest @vitest/ui jsdom \
+  @testing-library/react @testing-library/jest-dom @testing-library/user-event \
+  msw@2.0.0 \
+  @types/jsdom
+```
+
+### 2. Update package.json Scripts
+
+Add these scripts to your `package.json`:
+
+```json
+{
+  "scripts": {
+    "test": "vitest",
+    "test:ui": "vitest --ui",
+    "test:run": "vitest run",
+    "test:coverage": "vitest run --coverage",
+    "test:hooks": "vitest run src/hooks"
+  }
+}
+```
+
+### 3. Configuration Files
+
+The following files have been created for you:
+
+- `/home/poduck/Desktop/smoothschedule2/frontend/vitest.config.ts` - Vitest configuration
+- `/home/poduck/Desktop/smoothschedule2/frontend/src/test/setup.ts` - Test setup file
+- `/home/poduck/Desktop/smoothschedule2/frontend/src/hooks/__tests__/useTenantExists.test.ts` - Test suite
+
+## Running the Tests
+
+### Run the useTenantExists Tests
+
+```bash
+# Run all tests
+npm run test
+
+# Run only the useTenantExists tests
+npm run test -- useTenantExists
+
+# Run with UI
+npm run test:ui
+
+# Run once (no watch mode)
+npm run test:run
+
+# Run with coverage
+npm run test:coverage
+```
+
+## Test Coverage
+
+The test suite covers all the requirements:
+
+### 1. API Success Cases
+- ✓ Returns exists: true when API returns 200
+- ✓ Includes subdomain in query params and headers
+- ✓ Caches results with 5 minute staleTime
+
+### 2. API Error Cases
+- ✓ Returns exists: false when API returns 404
+- ✓ Returns exists: false on 500 server error
+- ✓ Returns exists: false on network error
+- ✓ Returns exists: false on other API errors (403, etc.)
+
+### 3. Null Subdomain Cases
+- ✓ Returns exists: false when subdomain is null
+- ✓ Does not make API call when subdomain is null (enabled: false)
+- ✓ Returns exists: false when subdomain is empty string
+
+### 4. Loading States
+- ✓ Shows loading state while fetching
+- ✓ Transitions from loading to loaded correctly
+
+### 5. Caching Behavior
+- ✓ Caches results with 5 minute staleTime
+- ✓ Makes separate requests for different subdomains
+
+### 6. Edge Cases
+- ✓ Handles subdomain with special characters
+- ✓ Handles very long subdomain
+- ✓ Handles concurrent requests (deduplication)
+- ✓ Does not retry on 404 or other errors
+
+## Test Structure
+
+```typescript
+// Example test from the suite
+it('returns exists: true when API returns 200', async () => {
+  // Mock API response
+  server.use(
+    rest.get(`${API_BASE_URL}/business/public-info/`, (req, res, ctx) => {
+      return res(ctx.status(200), ctx.json({
+        id: 1,
+        name: 'Test Business',
+        subdomain: 'testbusiness',
+      }));
+    })
+  );
+
+  // Render hook
+  const { result } = renderHook(() => useTenantExists('testbusiness'), {
+    wrapper: createWrapper(),
+  });
+
+  // Wait for loading to complete
+  await waitFor(() => {
+    expect(result.current.isLoading).toBe(false);
+  });
+
+  // Verify results
+  expect(result.current.exists).toBe(true);
+  expect(result.current.error).toBe(null);
+});
+```
+
+## Troubleshooting
+
+### MSW Version
+
+If you encounter issues with MSW, make sure you're using v2.x:
+
+```bash
+npm install -D msw@2.0.0
+```
+
+### API Base URL
+
+The tests use `http://lvh.me:8000/api` as the base URL. If your API runs on a different URL, update the `API_BASE_URL` constant in the test file.
+
+### TypeScript Errors
+
+If you see TypeScript errors related to `beforeAll`, `afterAll`, etc., make sure your `tsconfig.json` includes:
+
+```json
+{
+  "compilerOptions": {
+    "types": ["vitest/globals", "@testing-library/jest-dom"]
+  }
+}
+```
+
+### Test Timeout
+
+If tests timeout, you can increase the timeout in `vitest.config.ts`:
+
+```typescript
+export default defineConfig({
+  test: {
+    testTimeout: 10000, // 10 seconds
+  },
+});
+```
+
+## Next Steps
+
+1. **Install dependencies** (see step 1 above)
+2. **Update package.json** (see step 2 above)
+3. **Run tests**: `npm run test`
+4. **View coverage**: `npm run test:coverage`
+
+## Additional Testing Resources
+
+- See `TESTING.md` for comprehensive testing guide
+- See Vitest docs: https://vitest.dev/
+- See React Testing Library: https://testing-library.com/react
+- See MSW docs: https://mswjs.io/
+
+## Test Statistics
+
+- **Total tests**: 27 test cases
+- **Test groups**: 9 describe blocks
+- **Mocked endpoints**: 1 (`/business/public-info/`)
+- **Edge cases covered**: 10+