ci(release): idempotent registry publish — survive re-tagged releases

A moved release tag re-fires the publish workflows, and the Gitea
registries reject duplicate uploads with 409 (deb pool, rpm group, and
the generic packages' versioned URLs; the channel aliases already
pre-deleted). Delete any prior copy of the exact version before
uploading (404 on first publish tolerated), so a republished tag
overwrites instead of wedging — v0.5.0's retag left stale no-port-change
artifacts published and every re-run red.

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

.gitea/workflows/flatpak.yml

@@ -133,7 +133,10 @@ jobs:
           TOKEN: ${{ secrets.REGISTRY_TOKEN }}
         run: |
           BASE="https://$REGISTRY/api/packages/$OWNER/generic/$PACKAGE"
-          # 1) Immutable, versioned URL.
+          # 1) Versioned URL. A re-tagged release re-fires this workflow and the registry 409s on
+          #    duplicate uploads — delete any prior copy first (404 on the first publish is fine).
+          curl -fsS -o /dev/null --user "enricobuehler:$TOKEN" -X DELETE \
+            "$BASE/$VERSION/$BUNDLE" || true
           curl -fsS --user "enricobuehler:$TOKEN" --upload-file "$BUNDLE" \
             "$BASE/$VERSION/$BUNDLE"
           echo "published $BASE/$VERSION/$BUNDLE"