A repository's branches list's Server-Timing names its phases: session, each read, render #3396

The branches list now answers with a Server-Timing header naming session, branches, refs and render, after the usual app. It uses notePhase and timePhaseAsync the same way boards-view.ts does.

• Reads: the page makes two reads. branches is the ahead/behind listing plus tip commits. refs is the ref set that feeds the create-branch form. They still run in parallel through the same Promise.all, so order and errors are unchanged.
• Scope: the change is in renderBranches in src/web/pages/branches.ts, so a live browse of an origin's branches gets the same header as a local repository.
• Unchanged: the body, status codes and caching.
• Test: test/branches-timing.test.ts requests the page signed in and asserts each phase name appears with a duration. It would fail without the change.
• Checks: the new test and the other branch tests pass. I could not run bun x tsc --noEmit here because bun cannot write to its tempdir in this sandbox, so the type check is unrun.
• Left out: I did not split branches into the listing and the tip-commit reads. The issue asked for one phase per data read, and this is one call.

To try it, open /:owner/:name/branches and read the Server-Timing response header.

Closes #3278

The branches list now answers with a Server-Timing header naming session, branches, refs and render, after the usual app. It uses notePhase and timePhaseAsync the same way boards-view.ts does.

• Reads: the page makes two reads. branches is the ahead/behind listing plus tip commits. refs is the ref set that feeds the create-branch form. They still run in parallel through the same Promise.all, so order and errors are unchanged.
• Scope: the change is in renderBranches in src/web/pages/branches.ts, so a live browse of an origin's branches gets the same header as a local repository.
• Unchanged: the body, status codes and caching.
• Test: test/branches-timing.test.ts requests the page signed in and asserts each phase name appears with a duration. It would fail without the change.
• Checks: the new test and the other branch tests pass. I could not run bun x tsc --noEmit here because bun cannot write to its tempdir in this sandbox, so the type check is unrun.
• Left out: I did not split branches into the listing and the tip-commit reads. The issue asked for one phase per data read, and this is one call.

To try it, open /:owner/:name/branches and read the Server-Timing response header.

I fixed the header in test/branches-timing.test.ts. It now says the page names session, branches, refs and render, and cites #3278 instead of #3281.

I also ran the type check, which earlier couldn't run here. It now passes with no errors. The earlier failure came from bun being unable to write to its tempdir. Pointing BUN_TMPDIR and the install cache at a writable directory under $TMPDIR fixed that, and bun install then ran. The branches timing test still passes. The page code is unchanged.