Add internal org chat (phase 1) with DM, groups, and org settings.

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/conversations/chat-user-id.util.ts

@@ -0,0 +1,10 @@
+/** شناسه پایدار کاربر در سرویس چت خارجی (scoped به org) */
+export function buildChatUserId(organizationId: string, userId: string): string {
+  const o = organizationId.replace(/-/g, '').slice(0, 12);
+  const u = userId.replace(/-/g, '').slice(0, 12);
+  return `m${o}u${u}`;
+}
+
+export function dmPairKey(userA: string, userB: string): [string, string] {
+  return userA < userB ? [userA, userB] : [userB, userA];
+}