Publish a fixed-URL "latest" AppImage for static-URL updaters

Gitea has no /releases/latest/download/ redirect and release URLs always
include the tag, so updaters that poll a constant URL (Shelly) cannot use
them. After publishing a vX.Y.Z release, replace the asset on a rolling
pre-release tagged "latest":

  .../releases/download/latest/WhatsThatMusic-latest-linux-x86_64.AppImage

Replacing the asset changes its ETag and Last-Modified, which Shelly
compares. The pre-release flag keeps Gitea's own "latest release" on the
newest vX.Y.Z. The logic lives in .gitea/scripts/update-latest.sh so it can
be run against the API outside CI. The publish job now checks out first,
since checkout cleans the workspace and would delete downloaded artifacts.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

.gitea/scripts/update-latest.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+# Maintains a rolling "latest" release whose AppImage always has the same
+# download URL, for updaters that poll a static URL (e.g. Shelly) instead of
+# understanding version tags:
+#
+#   <server>/<owner>/<repo>/releases/download/latest/WhatsThatMusic-latest-linux-x86_64.AppImage
+#
+# Gitea serves ETag and Last-Modified on release assets, and replacing the
+# asset changes both, which is how those updaters detect a new build.
+# Gitea has no GitHub-style /releases/latest/download/ redirect, hence this.
+#
+# Marked as a pre-release so Gitea's own "latest release" stays the newest vX.Y.Z.
+#
+# Required env: TOKEN, API (…/api/v1/repos/<owner>/<repo>), GITHUB_REF_NAME, GITHUB_SHA
+# Optional env: ARTIFACTS_DIR (default: artifacts)
+set -euo pipefail
+
+: "${TOKEN:?TOKEN is required}" "${API:?API is required}"
+: "${GITHUB_REF_NAME:?GITHUB_REF_NAME is required}" "${GITHUB_SHA:?GITHUB_SHA is required}"
+ARTIFACTS_DIR="${ARTIFACTS_DIR:-artifacts}"
+LATEST_TAG="latest"
+LATEST_NAME="WhatsThatMusic-latest-linux-x86_64.AppImage"
+
+api() {
+  local method="$1" path="$2"; shift 2
+  local out code body
+  out=$(curl -s -w '\n%{http_code}' -X "$method" -H "Authorization: token $TOKEN" "$API$path" "$@")
+  code=$(printf '%s' "$out" | tail -n1)
+  body=$(printf '%s' "$out" | sed '$d')
+  if [ "$code" -ge 400 ]; then
+    echo "$method $path -> HTTP $code" >&2
+    echo "$body" >&2
+    return 1
+  fi
+  printf '%s' "$body"
+}
+
+appimage=$(find "$ARTIFACTS_DIR" -type f -name '*.AppImage' | sort | head -n1)
+if [ -z "$appimage" ]; then
+  echo "No AppImage under $ARTIFACTS_DIR; cannot update the $LATEST_TAG release." >&2
+  exit 1
+fi
+
+body_json=$(node -e '
+  console.log(JSON.stringify({
+    body: "Rolling pointer to the newest AppImage, currently " + process.argv[1] + ". " +
+          "The download URL for this asset never changes; versioned downloads are on each vX.Y.Z release.",
+  }));' "$GITHUB_REF_NAME")
+
+rolling_id=$(api GET "/releases/tags/$LATEST_TAG" 2>/dev/null \
+  | node -pe "JSON.parse(require('fs').readFileSync(0,'utf8')).id" 2>/dev/null || true)
+
+if [ -z "${rolling_id:-}" ]; then
+  echo "No '$LATEST_TAG' release yet; creating it."
+  create_json=$(node -e '
+    console.log(JSON.stringify({
+      tag_name: "latest", name: "Latest (rolling)", target_commitish: process.argv[1],
+      prerelease: true, body: JSON.parse(process.argv[2]).body,
+    }));' "$GITHUB_SHA" "$body_json")
+  rolling_id=$(api POST "/releases" -H "Content-Type: application/json" -d "$create_json" \
+    | node -pe "JSON.parse(require('fs').readFileSync(0,'utf8')).id")
+else
+  api PATCH "/releases/$rolling_id" -H "Content-Type: application/json" -d "$body_json" >/dev/null
+fi
+
+# Replace the asset: the new upload gets a new ETag and Last-Modified.
+old_id=$(api GET "/releases/$rolling_id/assets" \
+  | node -pe "((JSON.parse(require('fs').readFileSync(0,'utf8'))).find(a => a.name === process.argv[1]) || {}).id || ''" "$LATEST_NAME")
+if [ -n "$old_id" ]; then
+  api DELETE "/releases/$rolling_id/assets/$old_id" >/dev/null
+fi
+
+echo "Uploading $LATEST_NAME from $(basename "$appimage") ($(du -h "$appimage" | cut -f1))"
+api POST "/releases/$rolling_id/assets?name=$LATEST_NAME" -F "attachment=@$appimage" >/dev/null
+echo "Updated '$LATEST_TAG' release ($rolling_id) to $GITHUB_REF_NAME"