release script: require the tag to exist before creating a release

Letting the release API auto-create the tag leaves a forge-only tag the
push-mirror prunes on its next sync — and Forgejo demotes the release
to a hidden draft when its tag disappears (this made v1.0.2 vanish from
the releases page overnight). Fail with instructions instead.

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

apps/desktop/scripts/release-codeberg.mjs

@@ -57,6 +57,17 @@ async function api(path, init = {}) {
 async function getOrCreateRelease(tagName, { prerelease = false } = {}) {
     let res = await api(`/repos/${OWNER}/${REPO}/releases/tags/${encodeURIComponent(tagName)}`);
     if (res.status === 404) {
+        // The tag MUST already exist on the forge, arriving via the git.utn.lol
+        // push-mirror. If we let the release API auto-create it, the next mirror
+        // sync prunes the forge-only tag and Forgejo silently demotes the release
+        // to a hidden draft (this ate v1.0.2's release page overnight).
+        const tagRes = await api(`/repos/${OWNER}/${REPO}/tags/${encodeURIComponent(tagName)}`);
+        if (tagRes.status === 404) {
+            throw new Error(
+                `Tag ${tagName} not found on ${OWNER}/${REPO}. Push it to the source repo first ` +
+                    `(git push origin ${tagName}) and wait for the mirror to sync.`,
+            );
+        }
         res = await api(`/repos/${OWNER}/${REPO}/releases`, {
             method: "POST",
             headers: { "Content-Type": "application/json" },