feat(contracts): Add legal export package and ESIGN compliance improvements

- Add export_legal endpoint for signed contracts that generates a ZIP with:
  - Signed contract PDF
  - Audit certificate PDF with signature details and hash verification
  - Machine-readable signature_record.json
  - Integrity verification report
  - README documentation

- Add audit certificate template with:
  - Contract and signature information
  - Consent records with exact legal text
  - Document integrity verification (SHA-256 hash comparison)
  - ESIGN Act and UETA compliance statement

- Update ContractSigning page for ESIGN/UETA compliance:
  - Consent checkbox text now matches backend-stored legal text
  - Added proper legal notice with ESIGN Act references

- Add signed_at field to ContractListSerializer
- Add view/print buttons for signed contracts in Contracts page
- Allow viewing signed contracts via public signing URL

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

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

frontend/src/i18n/locales/en.json

@@ -70,7 +70,28 @@
     "rememberMe": "Remember me",
     "twoFactorRequired": "Two-factor authentication required",
     "enterCode": "Enter verification code",
-    "verifyCode": "Verify Code"
+    "verifyCode": "Verify Code",
+    "login": {
+      "title": "Sign in to your account",
+      "subtitle": "Don't have an account?",
+      "createAccount": "Create one now",
+      "platformBadge": "Platform Login",
+      "heroTitle": "Manage Your Business with Confidence",
+      "heroSubtitle": "Access your dashboard to manage appointments, customers, and grow your business.",
+      "features": {
+        "scheduling": "Smart scheduling & resource management",
+        "automation": "Automated reminders & follow-ups",
+        "security": "Enterprise-grade security"
+      },
+      "privacy": "Privacy",
+      "terms": "Terms"
+    },
+    "tenantLogin": {
+      "welcome": "Welcome to {{business}}",
+      "subtitle": "Sign in to manage your appointments",
+      "staffAccess": "Staff Access",
+      "customerBooking": "Customer Booking"
+    }
   },
   "nav": {
     "dashboard": "Dashboard",
@@ -679,6 +700,7 @@
       "edit": "Edit",
       "viewDetails": "View Details",
       "copyLink": "Copy Signing Link",
+      "copied": "Copied!",
       "sendEmail": "Send Email",
       "openSigningPage": "Open Signing Page",
       "saveChanges": "Save Changes"
@@ -723,7 +745,11 @@
       "status": "Status",
       "created": "Created",
       "contentPreview": "Content Preview",
-      "signingLink": "Signing Link"
+      "signingLink": "Signing Link",
+      "signedTitle": "Contract Successfully Signed",
+      "viewFullContract": "View Full Contract",
+      "printContract": "Print Contract",
+      "exportLegal": "Export Legal Package"
     },
     "preview": {
       "title": "Preview Contract",
@@ -861,7 +887,14 @@
     "noCustomersFound": "No customers found matching your search.",
     "addNewCustomer": "Add New Customer",
     "createCustomer": "Create Customer",
-    "errorLoading": "Error loading customers"
+    "errorLoading": "Error loading customers",
+    "deleteCustomer": "Delete Customer",
+    "deleteConfirmation": "Are you sure you want to delete this customer? This action cannot be undone.",
+    "password": "Password",
+    "newPassword": "New Password",
+    "passwordPlaceholder": "Leave blank to keep current password",
+    "accountInfo": "Account Information",
+    "contactDetails": "Contact Details"
   },
   "resources": {
     "title": "Resources",