fix(pack): valid manifest YAML, stable-release picker, tolerant asset re-upload

- manifest: single-quote the coa-template note - nested double quotes
  made the scalar invalid YAML (awk include-parser unaffected; it only
  reads repo:/include: lines)
- build_pack: releases?limit=1 could hand back a prerelease/draft;
  fetch limit=10 and jq-select the first stable release
- release.yml: re-running for an existing tag 409'd on duplicate asset
  names and set -euo pipefail killed the job; skip already-attached
  assets / warn on failed uploads and only fail when the release ends
  up with zero assets

manifest.yaml

@@ -12,7 +12,7 @@ addons:
 
   - repo: coa-template             # template-only — not an installable addon
     include: false
-    note: "Gitea "Use This Template" source repo for new coa-* forks."
+    note: 'Gitea "Use This Template" source repo for new coa-* forks.'
 
   - repo: coa-ai-voiceover
     include: false