AXI-168: Make MCP Delivery lifecycle session-scoped

[Codename-11]

Summary

• separate generic MCP connection presence from individual Delivery session liveness
• keep quiet-session recovery requests open until the exact WorkSession produces lifecycle evidence
• add owner-scoped workSessions.abandon for no-output direct-MCP delivery sessions
• prevent direct MCP Execute runs from completing while their Delivery session is unbound and still active or stale
• return explicit lifecycle next actions from MCP run/session tools while preserving the compact default tool budget

Root cause

Generic MCP traffic refreshed an AgentConnection and cleared recovery requests for every WorkSession owned by that connection, without refreshing those sessions. The stale sweep could therefore recreate the same requests. Direct MCP runs could also complete while a Claimed/In Progress Delivery session had neither an implementation PR nor an explicit terminal disposition.

Validation

• pnpm lint (passes; existing repository warnings only)
• pnpm typecheck
• focused Vitest: 27/27 passed
• full serialized Vitest against disposable local Postgres/Redis: 1,525 passed, 1 skipped

No schema migration, release, or deployment is included.