Add the frame-beta-2 release notes

The second beta brings the one-command installer and the README quick
start; the game and Dawn are unchanged since frame-beta-1. The release
workflow's manual run now defaults to this tag.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019HBRGKTE1GnN2ah8gcZKr3

.github/workflows/frame-release.yml

@@ -12,7 +12,7 @@ on:
       tag:
         description: Release tag, frame-<something>; docs/releases/<tag>.md holds its notes
         required: true
-        default: frame-beta-1
+        default: frame-beta-2
 permissions:
   contents: write
 jobs: