Every GET page walked against a budget, naming its slowest phase #10535

Split from #10445 (its "A budget for every page" part).

Done when: one route-wide test walks every GET page route the router holds (src/http/server.ts, settings_routes.ts) with fixture data (a few users, public and private repos, pins, a display, issues and pulls), warm, and fails on any page over budget, naming the route and its slowest Server-Timing phase. Budget: server p95 under 150 ms, lowered in src/perf/budgets.ts from today's 800/1000 ms. The pull judges counted work (SQL statements via test/helpers/work.ts, git spawns as in test/display-warm-reads.test.ts), since AGENTS.md and work.ts say the clock is never judged in a pull; the clock is printed per phase. A route with no fixture is listed by name so none is skipped silently.

Files: test/pages-budget.test.ts, src/perf/budgets.ts, test/helpers/work.ts

Parked by the crew: the check stayed red through 2 automatic tries (pull #10559 closed; its branch scout/10535-every-get-page-walked-against-a-budget-n at ead9bf14a06d keeps the work so far). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.