codeSplitters privacy: cover Cloudflare request logs, and back the 'we'll tell you about changes' promise #516

Two loose ends on the #/privacy page (#500):

1. It doesn't mention Cloudflare's own request logs (Workers logs and observability, and our console.error lines). Check what's on for the codesplitters Worker and how long it's kept, then add a row to the 'What we found' table.
2. It promises 'If this page changes in a way that matters, we'll say so on the site before it applies,' but there's no way to show that notice. A dismissable banner fed by a dated entry would do it (one flag in features.json or a var).