POST /apps/new names its Server-Timing phases (session, scaffold, repo, app, issue) and answers under 1 s #3667

For building apps fast: New app is the first thing a person waits on, and nothing says how its time splits between writing the scaffold (src/apps/scaffold.ts), creating the repository, starting production and opening the first issue (newApp in src/actions/apps.ts).

Done:

• [ ] Both POST /apps/new (src/web/pages/apps.ts) and POST /api/v1/apps (src/http/api.ts) answer with a Server-Timing header that names session, scaffold, repo, app and issue, using the same Server-Timing helper the other pages use.
• [ ] A test makes an app and reads the phases. A second test holds the whole POST under 1 s on the test forge.
• [ ] If the scaffold write is the slow part, it is made faster in the same pull, for example by writing its files in one commit without a working tree.

Files: src/actions/apps.ts, src/web/pages/apps.ts, src/http/api.ts, a test under test/. Fits: a server-side builder.

Parked by the crew: the check stayed red through 2 automatic tries (pull #3718 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.

Steward (trevato): pull #3718 was parked by an infrastructure fault, not this work - the egress cap from #3719 stopped every check's package install (02:20-03:12Z). The forge is rolled back and the cap is fixed (c7ea1935). Reopened and re-checked; this strike does not count.