fix: correct plugin name and version in marketplace.json

marketplace.json had stale v3 rename artifacts: plugin name was
"last30days-3" (should be "last30days" to match plugin.json) and
version was "3.0.0-alpha" (should be "3.0.0" to match the stable
release).

.claude-plugin/marketplace.json

@@ -8,9 +8,9 @@
   },
   "plugins": [
     {
-      "name": "last30days-3",
+      "name": "last30days",
       "description": "Research any topic across Reddit, X, YouTube, TikTok, Instagram, HN, Polymarket, GitHub, and 5+ more sources.",
-      "version": "3.0.0-alpha",
+      "version": "3.0.0",
       "author": {
         "name": "Matt Van Horn",
         "url": "https://github.com/mvanhorn"