feat: 10 quick wins — account deletion, health check, debug cleanup, UX polish, graceful shutdown

- backend/handlers/user/account.go: Wire DELETE /api/user/account to call
  anonymize_user() for registered users and delete_guest_user() for guests,
  with CardDAV contact cleanup
- backend/handlers/user/profile_test.go: Add TestAccount_DeleteGuest and
  enhance TestAccount_Delete to verify anonymization results
- backend/main.go: Add GET /api/health endpoint with DB ping and S3 status
  check; add HSTS and Referrer-Policy security headers; replace
  http.ListenAndServe with http.Server + graceful SIGTERM/SIGINT shutdown
- frontend/routes/+layout.svelte: Replace alert() with toast notifications
  for email verification flow
- frontend/routes/login/+page.svelte: Replace alert() with toast.info for
  social login prototype buttons
- frontend/booking/BookingFlow.svelte: Remove 2 console.log debug calls;
  add cancellation policy note in Step 3; add timezone policy comment
- frontend/ImageUpload.svelte: Comment out debug console.log
- init-scripts/init-script.sql: Add delete_guest_user() SQL function
- docs: Update README.md and Obsidian notes to reflect completed items

frontend/src/routes/+layout.svelte

@@ -3,6 +3,7 @@
 	import favicon from '$lib/assets/favicon.svg';
 	import NavBar from '$lib/components/layout/NavBar.svelte';
 	import { Toaster } from '$lib/components/ui/sonner/index.js';
+	import { toast } from 'svelte-sonner';
 	import { authStore } from '$lib/stores/auth.svelte';
 	import { onMount } from 'svelte';
 
@@ -30,15 +31,16 @@
 
 	// Verify email address
 	async function verify_email() {
-		alert('Verifying email address...');
+		const loadingToast = toast.loading('Verifying email address...');
 		const response = await fetch('/api/verify-email', {
 			method: 'POST'
 		});
 
 		if (response.ok) {
+			toast.success('Email verified successfully!', { id: loadingToast });
 			window.location.reload();
 		} else {
-			alert('Failed to verify email address');
+			toast.error('Failed to verify email address', { id: loadingToast });
 		}
 	}
 </script>

frontend/src/routes/login/+page.svelte

@@ -253,7 +253,7 @@
 	}
 
 	function handleSocialLogin(provider: string) {
-		alert(`${provider} login clicked! (This is just a prototype)`);
+		toast.info(`${provider} login coming soon`);
 	}
 
 	// when password changes, re-compute strength