fix(release): repack the zip root-level for the Composer registry; make release steps idempotent

Gitea's registry answered 400 'composer.json file is missing' for the shopware-cli zip
(single top-level folder). Repack the same prebuilt content with composer.json at the root.
Drop the tag-exists skip guard so a half-finished release can be re-run; reuse an existing
release/asset. Bump to 0.1.1.

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

composer.json

@@ -3,7 +3,7 @@
     "description": "Export database dumps for Shopware 6 environments.",
     "type": "shopware-platform-plugin",
     "license": "MIT",
-    "version": "0.1.0",
+    "version": "0.1.1",
     "keywords": [
         "shopware",
         "shopware6",