Invitation system: DB + API + landing page + share links

- invitations table (token, task, inviter, expiry 7d)
- POST /invitations (create + share links: WhatsApp, Telegram, SMS, Copy)
- GET /invite/:token (public landing page)
- POST /invite/:token/accept (register + assign + JWT)
- Landing page at /invite/[token] with accept flow
- CLAUDE.md + Notion key deployed to all servers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/tasks/lib/api.ts

@@ -303,3 +303,44 @@ export function sendCollabRequest(token: string, taskId: string, data: { to_user
 export function searchUsers(token: string, query: string) {
   return apiFetch<{ data: { id: string; name: string; email: string; avatar_url: string | null }[] }>(`/api/v1/auth/users/search?q=${encodeURIComponent(query)}`, { token });
 }
+
+// Invitations
+export interface Invitation {
+  id: string;
+  token: string;
+  task_id: string;
+  inviter_id: string | null;
+  invitee_email: string | null;
+  invitee_name: string | null;
+  message: string;
+  status: string;
+  expires_at: string;
+  accepted_at: string | null;
+  created_at: string;
+}
+
+export interface InvitationResponse {
+  invitation: Invitation;
+  link: string;
+  share: {
+    whatsapp: string;
+    telegram: string;
+    sms: string;
+    copy: string;
+  };
+}
+
+export function createInvitation(
+  token: string,
+  data: { task_id: string; invitee_email?: string; invitee_name?: string; message?: string; inviter_id?: string }
+) {
+  return apiFetch<{ data: InvitationResponse }>("/api/v1/invitations", { method: "POST", body: data, token });
+}
+
+export function getTaskInvitations(token: string, taskId: string) {
+  return apiFetch<{ data: Invitation[] }>(`/api/v1/tasks/${taskId}/invitations`, { token });
+}
+
+export function revokeInvitation(token: string, invitationId: string) {
+  return apiFetch<{ data: Invitation }>(`/api/v1/invitations/${invitationId}`, { method: "DELETE", token });
+}