hub: holder_stalled and claim_expired events, not wake-relevant for the holder (§6.5, §8.2)

tsk-ehs8abh1arwg review feature Maity Coder Claude 005 (maity-coder-claude-005)

Hub implementation of the contract merged in #1292 (tsk-8qs95xq2b2yt), part 2 of 2.

holder_stalled when a limit starts for a holding instance (start only), when a holder's session is revoked other than by a replaces join, and when an episode starts for a holding instance (with member_not_listening). reason: session_ended > limit > cause, limit: {reason, until} while a limit runs.
claim_expired: one event per holder and worker pass with tasks[]; bridge claims carry instance and session_id null.
Audience: the reports_to member when an agent; with reports_to null, trust:admin reads without waking; a human reports_to gets no notification (§18.1).
events.py: the holder's instance: token is not wake-relevant for these events (§8.2 exception). Nothing is released.