feat(frontend): add PhoneInput component with UK validation

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

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

frontend/src/lib/components/ui/phone-input/PhoneInput.svelte

@@ -0,0 +1,103 @@
+<script lang="ts">
+	import { Input } from '$lib/components/ui/input/index.js';
+	import { isValidUKPhone, formatPhoneDisplay } from '$lib/utils/phone';
+
+	interface Props {
+		value?: string;
+		error?: string;
+		placeholder?: string;
+		required?: boolean;
+		disabled?: boolean;
+		class?: string;
+		id?: string;
+		onvaluechange?: (value: string) => void;
+		onerrorchange?: (error: string) => void;
+	}
+
+	let {
+		value = $bindable(''),
+		error = $bindable(''),
+		placeholder = '07123 456789 or +44 7123 456789',
+		required = false,
+		disabled = false,
+		class: className = '',
+		id = 'phone',
+		onvaluechange,
+		onerrorchange
+	}: Props = $props();
+
+	let touched = $state(false);
+
+	function handleKeyDown(e: KeyboardEvent) {
+		const target = e.target as HTMLInputElement;
+		const allowedKeys = ['Backspace', 'Delete', 'Tab', 'ArrowLeft', 'ArrowRight', 'ArrowUp', 'ArrowDown', 'Home', 'End'];
+		if (allowedKeys.includes(e.key)) return;
+		if (e.key === '+') return;  // allow + anywhere; normalisePhoneInput removes extras
+		if (!/^[0-9]$/.test(e.key)) {
+			e.preventDefault();
+		}
+	}
+
+	function normalizePhone(value: string): string {
+		let cleaned = value.replace(/[\s\-\(\)]/g, '');
+		if (cleaned.startsWith('07')) {
+			cleaned = '+44' + cleaned.substring(1);
+		}
+		return cleaned;
+	}
+
+	function handleInput(e: Event) {
+		const target = e.target as HTMLInputElement;
+		const formatted = formatPhoneDisplay(target.value);
+		value = formatted;
+		onvaluechange?.(formatted);
+		// Only show live validation after the field has been blurred at least once
+		if (touched) {
+			if (formatted && !isValidUKPhone(formatted)) {
+				error = 'Invalid UK phone number';
+				onerrorchange?.(error);
+			} else {
+				error = '';
+				onerrorchange?.('');
+			}
+		}
+	}
+
+	function handleBlur() {
+		touched = true;
+		if (value && !isValidUKPhone(value)) {
+			error = 'Invalid UK phone number';
+			onerrorchange?.(error);
+		} else {
+			error = '';
+			onerrorchange?.('');
+			if (value) {
+				const normalized = normalizePhone(value);
+				if (normalized !== value) {
+					value = normalized;
+					onvaluechange?.(normalized);
+				}
+			}
+		}
+	}
+</script>
+
+<div class="space-y-1.5">
+	<Input
+		{id}
+		type="text"
+		inputmode="tel"
+		{placeholder}
+		maxlength={15}
+		{value}
+		oninput={handleInput}
+		onblur={handleBlur}
+		onkeydown={handleKeyDown}
+		{disabled}
+		aria-invalid={!!error || undefined}
+		class={className}
+	/>
+	{#if error}
+		<p class="text-sm text-red-500">{error}</p>
+	{/if}
+</div>

frontend/src/lib/components/ui/phone-input/index.ts

@@ -0,0 +1,3 @@
+import PhoneInput from './PhoneInput.svelte';
+
+export { PhoneInput };

frontend/src/lib/utils/phone.ts

@@ -22,18 +22,18 @@ export function isValidUKPhone(phone: string): boolean {
 export function formatPhoneDisplay(value: string): string {
     const clean = normalisePhoneInput(value);
     if (clean.startsWith('+44')) {
-        const digits = clean.slice(3);
+        const digits = clean.slice(3).slice(0, 10);  // max 10 digits after +44
         if (digits.length <= 4) return '+44 ' + digits;
         if (digits.length <= 8) return '+44 ' + digits.slice(0, 4) + ' ' + digits.slice(4);
         return '+44 ' + digits.slice(0, 4) + ' ' + digits.slice(4, 10);
     }
     if (clean.startsWith('0')) {
-        const digits = clean.slice(1);
+        const digits = clean.slice(1).slice(0, 10);  // max 10 digits after 0
         if (digits.length <= 4) return '0' + digits;
         if (digits.length <= 7) return '0' + digits.slice(0, 4) + ' ' + digits.slice(4);
         return '0' + digits.slice(0, 4) + ' ' + digits.slice(4, 10);
     }
-    return clean;
+    return clean.slice(0, 15);  // fallback limit
 }
 
 /**