A repository's map page names its Server-Timing phases, and `/alice/forge/map` leaves the sweep's UNNAMED list #5766

Intent: the plan page (/:owner/:name/map) says where its time goes, as GET …/map has since #3320, so a slow map shows which phase is slow.

Done looks like:

• [ ] The page's Server-Timing header names session, the map read (graph, marks, pillars) and render, using the timing helper the other pages use.
• [ ] ["/alice/forge/map", "#3320"] leaves UNNAMED in test/server-timing-sweep.test.ts, and the sweep passes.
• [ ] A test asserts the page's header names each phase. It fails without the change.

Files: the map page under src/web/, test/server-timing-sweep.test.ts, a map timing test. Risks: none beyond timing overhead; the phases wrap reads that already happen.