Phase 1: Fix label lifecycle in gh_claim_issue and close-out path

[ericmmartin]

Problem

The label lifecycle has two gaps found during Phase 0 spike validation (issue #6):

1. gh_claim_issue never removes conductor:ready — after claiming, both conductor:ready and conductor:in-progress are present simultaneously.
2. Close-out path never removes conductor:in-progress — the spike comment + result-write path has no label cleanup, so conductor:in-progress lingers on closed issues.

Acceptance criteria

• gh_claim_issue removes conductor:ready after adding conductor:in-progress
• The work command's close-out path removes conductor:in-progress before adding conductor:done
• A closed issue ends up with exactly conductor:done (and no other conductor state labels)

Notes

Discovered during Phase 0 spike (commit 34fcdc4). Labels were manually tidied for issue #6.

semver: patch