feat(web): add lib/phone.ts with formatPhone/normalizePhone/zaloHref helpers

- Create apps/web/lib/phone.ts with VN_PHONE_REGEX, normalizePhone,
  formatPhone, and zaloHref helpers
- Deduplicate phone regex: auth.ts and inquiry.ts now import VN_PHONE_REGEX
  from @/lib/phone instead of defining their own local patterns
- Replace raw .replace(/^0/, '84') in inquiry-detail-dialog.tsx and
  lead-detail-dialog.tsx with zaloHref(); use formatPhone() for display

Resolves GOO-209

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

apps/web/lib/phone.ts

@@ -0,0 +1,59 @@
+/**
+ * Vietnamese phone number helpers.
+ *
+ * Regex covers the current VN numbering plan:
+ *   0[35789]x xxxxxxx — Viettel, Mobifone, Vinaphone, Gmobile, Indochina
+ *
+ * See: https://en.wikipedia.org/wiki/Telephone_numbers_in_Vietnam
+ */
+
+/** Matches a VN mobile number, with optional +84 or leading 0. */
+export const VN_PHONE_REGEX =
+  /^(0|\+84)(3[2-9]|5[2689]|7[06-9]|8[1-9]|9[0-9])\d{7}$/;
+
+/**
+ * Normalise a VN phone number to the E.164-ish form used by Zalo / APIs:
+ * strip leading 0 and prepend the country code (84).
+ *
+ * "0987654321" → "84987654321"
+ * "+84987654321" → "84987654321"
+ * "84987654321" → "84987654321"  (already normalised — idempotent)
+ */
+export function normalizePhone(phone: string): string {
+  const cleaned = phone.trim();
+  if (cleaned.startsWith('+84')) return `84${cleaned.slice(3)}`;
+  if (cleaned.startsWith('84')) return cleaned;
+  if (cleaned.startsWith('0')) return `84${cleaned.slice(1)}`;
+  return cleaned;
+}
+
+/**
+ * Format a raw VN phone number for display.
+ * Handles 10-digit numbers (0xx xxxx xxxx).
+ *
+ * "0987654321" → "0987 654 321"
+ * Passthrough for anything that doesn't match.
+ */
+export function formatPhone(phone: string): string {
+  const cleaned = phone.trim().replace(/\s+/g, '');
+
+  // 10-digit local format: 0xxx yyy zzz
+  const tenDigit = cleaned.match(/^(0\d{3})(\d{3})(\d{3})$/);
+  if (tenDigit) return `${tenDigit[1]} ${tenDigit[2]} ${tenDigit[3]}`;
+
+  // +84 prefix → treat as 10-digit local after swapping prefix
+  const e164 = cleaned.match(/^\+84(\d{9})$/);
+  if (e164) return formatPhone(`0${e164[1]}`);
+
+  return phone;
+}
+
+/**
+ * Returns the https://zalo.me deep-link URL for a given phone number.
+ *
+ * Zalo expects the number without a leading zero, prefixed with 84.
+ * "0987654321" → "https://zalo.me/84987654321"
+ */
+export function zaloHref(phone: string): string {
+  return `https://zalo.me/${normalizePhone(phone)}`;
+}

apps/web/lib/validations/auth.ts

@@ -1,6 +1,6 @@
 import { z } from 'zod';
 
-const phoneRegex = /^(0|\+84)(3[2-9]|5[2689]|7[06-9]|8[1-9]|9[0-9])\d{7}$/;
+import { VN_PHONE_REGEX as phoneRegex } from '@/lib/phone';
 
 export const loginSchema = z.object({
   phone: z

apps/web/lib/validations/inquiry.ts

@@ -1,12 +1,6 @@
 import { z } from 'zod';
 
-/**
- * Vietnamese phone number rule:
- * - 9–11 digits, optional leading +84 or 0.
- * We keep validation pragmatic: whitespace is stripped, then the remaining
- * string must be 9–11 digits (country code / leading zero stripped).
- */
-const PHONE_REGEX = /^(?:\+?84|0)?\d{9,11}$/;
+import { VN_PHONE_REGEX as PHONE_REGEX } from '@/lib/phone';
 
 export const inquiryFormSchema = z.object({
   message: z