feat(work-items): lease comments carry the phase of the work #11871

Problem

A lease says who holds an item, not what they are doing, so a claim for triage or discovery cannot
be told from an implementation claim, and per-phase durations cannot be measured.

Origin: D93, D94, Q515 (research R12 section 5: the lease carries phase=<kind>).

Fix

claim takes an optional --phase <kind> and writes it into the lease comment; absent means
implementation. reclaim and renew-lease keep it.

Done when

• The tracker CONTRACT's lease protocol documents the field and its values.
• Tests show claim --phase triage writes the field and renew-lease keeps it, for github and local-markdown, passing under scripts/run-test-file.sh; work-item-tracker.test.sh passes.
• A work-items changelog fragment passes bash scripts/check-changelog-fragments.sh.

Parent: #7578