fix(planning): add one round.sh command to hand an interview over after /clear #7761

Parent

Refs #5893

Depends on

• none: on the frontier now

Outcome

Taking over an interview after /clear is one documented command, and the old watcher's exit reads as a handover, not an error. Today the new session releases the old lease by hand (round.sh lease --release) and re-arms, and the displaced watcher's background task fails with exit 3 in the new conversation.

Owner decision recorded on #5893 (2026-10-12): "Item 6: what performs the lease handover after /clear?" → One round.sh command that releases the old lease and re-arms, with the displaced watcher exiting with a 'handed over' message.

Key interfaces

• round.py cmd_lease (only --release exists, no takeover) and the watcher's exit path.
• Interview skill surface.md, which documents the command.

Done when

• One round.sh command releases the old session's lease and re-arms for the new one (test).
• The displaced watcher exits with a message saying it was handed over, distinguishable from a failure (test in the watch suite).
• surface.md documents the command for the after-/clear case.
• The planning Python, surface and watch test suites pass.

Out of scope

• Other lease semantics.