✨ Invitations: show invite form when userFacing is enabled with open signup #4500

What — The account invitations view should show the invite form when user-facing invitations are enabled, even if public signup is open.
Why — The form is hidden behind the open-signup guard (#3833 informational alert), so deployments enabling the referral loop with open signup have no UI trigger.

Scope

• Gate: show the invite form when serverConfig.invitations.userFacing === true OR signup is closed (current behavior). Keep the informational alert only when signup is open AND the flag is off.
• Reads the flag from GET /api/auth/config (Node-side exposure tracked in Node#3981).
• Unit tests for the 3 states (closed-signup, open+flag, open+no-flag).

Depends on: pierreb-devkit/Node#3981.
Scope: validated 2026-07-24
Created via /dev:issue