Stop tracking MiniDapp build/ zips; keep latest-version downloads

Add .gitignore rule dapp/**/build/*.zip and untrack the two 2-demo build
artifacts. The published download remains dapp/2-demo/latest-version/.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: StablesCouncilExec

.gitignore

@@ -1,3 +1,5 @@
 node_modules/
 # When this tree is copied into the archived Pages checkout, never stage embedded git metadata
 _embedded_git/
+# MiniDapp build artifacts: the published download is dapp/<channel>/latest-version/, not the build/ subdir
+dapp/**/build/*.zip