refactor(frontend): migrate email fields to EmailInput component

Replace raw <Input type="email"> with <EmailInput> in login (register + login), account (gift card recipient), BookingFlow (guest email), and GiftCardsManagement (admin gift card email).

Removes 30-line validateEmail() function from login page (now handled by EmailInput internally).

Removes validateEmailFormat() from BookingFlow (EmailInput handles format validation; debounced backend email check preserved via onvaluechange/onblur).

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/lib/components/admin/GiftCardsManagement.svelte

@@ -4,6 +4,7 @@
 	import { Button } from '$lib/components/ui/button';
 	import * as Card from '$lib/components/ui/card';
 	import { Input } from '$lib/components/ui/input';
+	import { EmailInput } from '$lib/components/ui/email-input';
 	import * as Modal from '$lib/components/ui/dialog';
 	import { Skeleton } from '$lib/components/ui/skeleton';
 
@@ -1765,11 +1766,10 @@
 									Recipient Email Address (Optional)
 								{/if}
 							</label>
-							<Input
+							<EmailInput
 								id="generate-email"
-								type="email"
-								placeholder="e.g. customer@example.com"
 								bind:value={generateEmail}
+								placeholder="e.g. customer@example.com"
 							/>
 							{#if selectedCustomer?.email && !generateEmail.trim()}
 								<p class="text-xs text-gray-500 italic">Defaults to: {selectedCustomer.email}</p>