[ai] Refine Lead/Peer Role Exit Conditions to Align with Session Sunset

Context & Rationale The current .agents/skills/lead-role/references/lead-role-mode.md lists exit conditions stating the skill releases when "Shape has converged through dialogue and tickets/PRs are now appropriate".

This mechanism drops the agent out of the lead-role paradigm once implementation begins, effectively reactivating the standard "Auto Mode velocity-bias".

However, this conflicts with our intended session architecture where session-sunset (or explicit operator intervention) serves as the true exit boundary for an agent session's overarching operational mode. Dropping the role mid-session risks regressing into the blind "orchestrator-worker" paradigm precisely when executing the converged shape.

The same exit condition exists in .agents/skills/peer-role/references/peer-role-mode.md.

Proposed Action

1. Remove "shape convergence" as an exit condition from both lead-role-mode.md and peer-role-mode.md.
2. Consolidate the exit point to state the role persists for the duration of the session until a session-sunset triggers or the operator explicitly commands a role change.

Avoided Traps

• Leaving it as is: We risk agents losing the coordination mindset right as execution begins, leading to isolated implementation without continued peer awareness.