Live regions have addresses: fetch the region, not the page; 304 when unchanged #322

A page never reloads itself, and now a live region fetches only itself.

• layout.fragment hashes a fragment's bytes into an etag and answers if-none-match with 304 and no body.
• A live region may carry data-live-src: the home's shelf at /live/apps, On you at /live/on-you, the app page's Now at <repo>/app/now (studio/now.ts, lifted out of the page). The client fetches that address alone, conditionally, and swaps the region the fragment answers with; regions without an address still share one fetch of the page.
• Two renders that differ only in a relative time are the same region.
• checks: a failing test bun printed without a duration (as it does under CI for a test that took no time) is still named.

docs/STUDIO.md gains a Live regions section. Full suite green locally (1920 tests).