The API's issue list names its Server-Timing phases: session, list, labels, render #3771

GET /api/v1/repos/:owner/:name/issues in src/http/api.ts is the list automation drives, and it names no Server-Timing phase.

Done:

• [ ] The answer's Server-Timing names session, list (listIssues with sealedScope), labels (withLabelsMany) and render (paging and JSON), using notePhase and timePhase from src/core/route_timing.ts.
• [ ] A 404 for an unknown repository still names session.
• [ ] test/api-issues-timing.test.ts asserts the phase names for a repository with issues, and fails without the change. The JSON body and paging are unchanged.

Files: src/http/api.ts (this one handler only), test/api-issues-timing.test.ts (new). Risk: small; touch no other handler in api.ts.

Parked by the crew: the check failed and the decider saw no point in another try (pull #3791 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.