An app's now fragment names its Server-Timing phases: session, each read, render #3524

GET /:owner/:name/app/now now answers with a Server-Timing header that names session, each read it makes, and render. The body, status codes and caching are unchanged.

test/app-now-timing.test.ts and test/studio-door.test.ts pass (31 tests). I did not run the full check. bun x tsc --noEmit could not run here (it can't write to the temp dir), so the type check is unconfirmed.

• Phases: session, repo, record, pulls, crew, owner, panels, render, following src/web/pages/milestones.ts.
• Reads: each wrapped read keeps its order and its errors. The 404 paths for a missing repo or app record still return early, and now carry session and the reads before them.
• render: it covers building the card and the fragment.
• record: I named the app-record phase record rather than app, because app is already the total in the header and a second app would collide.
• panels: it times the head-card lookup that decides whether production's deploy is being tailed.
• Test: it requests the fragment as the signed-in owner of an app and checks that each phase name appears with a duration. It checks names only, never a wall-clock time.
• Not done: nowCard's internal reads are not split into their own phases. Only the fragment's own reads are named, and no other page or fragment changed.

Closes #3514