An issue page's Server-Timing names its phases: session, thread, links, render #3193

The issue page names its phases the way /map does (#3172), through notePhase/timePhase in src/core/route_timing.ts.

Done looks like:

• [ ] GET /:owner/:name/issues/:n sends server-timing with session, thread (comments and events), links (dependencies, pulls, teams) and render.
• [ ] A test fails if one is missing or if their sum is more than app.

Files: the issue page module under src/web/pages/, a test.