Program hosts tab should show pending (open) invitations, not just accepted ones

The global **Program hosts** tab currently only shows hosts who have accepted their invitation. Hosts with pending (sent but not yet accepted) invitations are not visible here.

To check open invitations, a program manager must currently open each program item individually and check its own hosts tab — impractical at scale.

## Requested behaviour

Add an "Open invitations" section or filter to the global program hosts tab, showing invitations that have been sent but not yet accepted, including:
- Which program item the invitation is for
- Who was invited (email / name if known)
- When the invitation was sent

## Background

Kompassi V1 had this view. Reported by Desucon Frostbite 2026 program management.