fix: throw on missing download URL; suppress ExperimentalWarning

- releaseAsset: if browser_download_url is absent after a successful
  upload (e.g. when the target repo has been renamed and the git remote
  still points to the old name), throw UploadError(MISSING_DOWNLOAD_URL)
  with a hint to use the full owner/repo#N target format instead of
  silently returning 'undefined' in the markdown output.

- cli/index: suppress Node's ExperimentalWarning for the Fetch API
  (emitted on Node < 21) so it doesn't pollute stdout/stderr.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Addono

src/cli/index.ts

@@ -5,6 +5,13 @@
  * CLI can be imported and tested without triggering `program.parse()`.
  */
 
+// Suppress ExperimentalWarning for the Fetch API (emitted on Node < 21).
+process.removeAllListeners("warning");
+process.on("warning", (warning) => {
+  if (warning.name === "ExperimentalWarning") return;
+  process.stderr.write(`${warning.stack ?? warning.message}\n`);
+});
+
 import { readFileSync } from "fs";
 import { dirname, resolve } from "path";
 import { fileURLToPath } from "url";

src/core/strategies/releaseAsset.ts

@@ -304,6 +304,15 @@ async function uploadAsset(
       },
     });
 
+    if (!asset.browser_download_url) {
+      throw new UploadError(
+        "Upload succeeded but no download URL was returned by GitHub. " +
+          "The target repository may have been renamed — use the full owner/repo#N target format.",
+        "MISSING_DOWNLOAD_URL",
+        { filePath, target },
+      );
+    }
+
     return asset.browser_download_url;
   } catch (err: unknown) {
     const status = getHttpStatus(err);