When parallel branches each rebuild a bundled JS file, rebuild instead of merging

If several feature branches each change the page source (e.g. TypeScript in a forked webview repo) and also commit the rebuilt, minified bundle (webview.js) plus a generated patch file, those built files will conflict on merge, and a hand merge of minified output is unsafe. Have whoever merges second rebuild the bundle and the patch from the combined source commits, and check the rebuilt bundle against the source diff. Record each branch's page-source commit SHA in its report so the rebuild has an exact input. Merge non-generated files (helper scripts, test runners) normally.