chore(site): empty announcements feed before banner ships

The welcome entry was test data for verifying the banner renders
end-to-end during development. Empty the array so the feature ships
with no banner showing by default — future announcements get added
deliberately, not because a placeholder slipped through.

The file stays in place (rather than getting deleted) so the URL
returns valid JSON and the poller's success path runs cleanly
instead of logging a 404 on every refresh.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: frenchie4111

site/public/announcements.json

@@ -1,10 +1,3 @@
 {
-  "announcements": [
-    {
-      "id": "welcome-2026-05",
-      "title": "Welcome to Harness! Star us on GitHub if you find this tool useful.",
-      "href": "https://github.com/frenchie4111/harness",
-      "publishedAt": "2026-05-25T00:00:00Z"
-    }
-  ]
+  "announcements": []
 }