package updates: Forgejo apk registry publishing + repo-config aport

CI publishes every locally built apk to the instance's Alpine registry
(catbot credentials via the PACKAGE_TOKEN secret; step skips until it
exists). catcrafts-fp6-repo ships the registry signing key and appends
the repo URL - NOT yet in extra_packages: the registry must have its
first content before image builds may reference it (an empty repo's
missing APKINDEX would break apk in the build chroots).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

aports/device/catcrafts-fp6-repo/catcrafts-fp6-repo.post-upgrade

@@ -0,0 +1,3 @@
+#!/bin/sh
+repo="https://forgejo.catcrafts.net/api/packages/Catcrafts/alpine/edge/fp6"
+grep -qxF "$repo" /etc/apk/repositories 2>/dev/null || echo "$repo" >> /etc/apk/repositories