Home's Server-Timing names its regions: feed, KPI row, pinned panels, shelf #3160

Part of #2675. Uses the phase seam from the /map issue before it.

Done:

• [ ] / records feed, kpis, panels and shelf (and cache hits as desc="hit" on the entry that hit).
• [ ] A test asserts the header on / for the owner carries those phases, and an anonymous / carries none of the admin-only ones.
• [ ] docs/CACHING.md 'Home' gains one bench run's per-region numbers.

Files: src/web/studio/home.ts (or wherever / assembles its regions), a test. Risk: do not record a phase for a region the viewer cannot see.