feat(GRO-1792): add recovery paths to booking error and cancellation pages

- Add "Start a new booking" button to BookingError linking to /admin/book
- Add "Book again" button to BookingCancelled linking to /admin/book
- Add business contact info section to BookingError (from BUSINESS_CONTACT_INFO constant)
- Replace hardcoded colors with CSS variables (--color-error, --color-cancelled, etc.)
- Add page-level string constants to eliminate hardcoded strings
- Add unit tests for both pages (9 tests passing)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/index.css

@@ -8,6 +8,19 @@
   --color-accent-dark: color-mix(in srgb, var(--color-accent) 78%, #000);
   --color-accent-light: color-mix(in srgb, var(--color-accent) 18%, #fff);
   --color-accent-lighter: color-mix(in srgb, var(--color-accent) 9%, #fff);
+
+  /* Semantic / booking page tokens */
+  --color-error: #dc2626;
+  --color-error-dark: #b91c1c;
+  --color-error-bg: #fef2f2;
+  --color-cancelled: #ea580c;
+  --color-cancelled-dark: #c2410c;
+  --color-cancelled-bg: #fff7ed;
+  --color-success: #16a34a;
+  --color-success-dark: #15803d;
+  --color-success-bg: #f0fdf4;
+  --color-text-secondary: #4b5563;
+  --color-surface: #fff;
 }
 
 *, *::before, *::after {