[P3] transitionIssueStatus multi-status-label dedupe edge case has no direct test

[itsmiso-ai]

Ask: Add a direct unit test for transitionIssueStatus covering the two-status-labels edge case it exists to fix.
Expected files: src/lib/issue-status.test.ts

Problem: src/lib/issue-status.ts documents that the helper exists because five API routes used to remove only the first status/* label, leaving stale labels on GitHub while the Prisma cache moved on. The helper's core guarantee — remove every existing status/* label, add exactly the target — is only exercised indirectly through route tests whose fixtures always start from a single status label. No test feeds it two status labels, so the exact regression the helper was written to prevent could return unnoticed. The file has no dedicated test suite at all.

Evidence:

• src/lib/issue-status.ts: transitionIssueStatus removes all status/* labels before adding the target
• src/app/api/issues/status/route.test.ts: fixtures are single-status only (["status/backlog"], ["status/in-progress"], ["priority/p0","status/backlog","type/bug"]); the multi-status case never appears
• No src/lib/issue-status.test.ts exists

Acceptance:

• A test calls transitionIssueStatus with labels containing two status/* entries (e.g. ["status/backlog","status/in-progress","type/bug"]) and asserts both are removed via removeIssueLabel and only the target is added
• Assert the returned label set is non-status labels + target
• Full suite still passes

[itsmiso-ai]

Promoting to ready. Acceptance is clear: add src/lib/issue-status.test.ts with a test that calls transitionIssueStatus with two status/* labels and asserts both are removed via removeIssueLabel and only the target is added, returning non-status labels + target.