GET /apps/new names its Server-Timing phases (session, each read, render) and answers under 50 ms #3681

For building apps fast: the New app form is the first page on the golden path. newAppPage in src/web/pages/apps.ts reads the person's orgs and every agent, and calls planningAvailable (src/crew/plan.ts), which runs Bun.which to look up the planner binary on every render. Nothing says what that costs.

Done:

• [ ] The page answers with a Server-Timing header that names session, each read (orgs, agents, planner) and render, using the helper the other pages' Server-Timing work uses.
• [ ] Whether the planner binary is present is looked up once and remembered for the process, not on every request. FORGE_APP_PLAN=0 still turns planning off.
• [ ] A test reads the phases. A second test holds the page under 50 ms with 50 agents on the forge.

Files: src/web/pages/apps.ts, src/crew/plan.ts, a test under test/. Fits: a page builder.