P7.2 #446: harden association lifecycle and event-driven traffic proof

[masarray]

Stacked lifecycle milestone for #446, based on P7.1 PR #459.

Why

The 7SX85 physical run proved the reporting data plane, but it also exposed a lifecycle weakness: the WPF shell still used ICMP Ping as an authoritative death signal and owned a second reconnect state machine on top of the per-IED MMS runtime.

That can falsely tear down a healthy IEC 61850 association when ICMP is filtered/rate-limited/transiently lost. It also made post-reconnect report proof vulnerable to stale HasReportStream state from the previous association and used a fixed 3 s delay for proof presentation.

Changes

• remove UI-owned ICMP death detection and duplicate reconnect ownership from MainWindow.P0AssociationLiveness.cs;
• keep MMS association/reconnect ownership exclusively in Iec61850MonitorRuntime, which already has bounded client cleanup, reconnect budgets and report re-arm staging;
• clear HasReportStream / report pulse whenever an association is marked offline and again when a replacement association installs;
• make InformationReport proof explicitly association-scoped;
• replace the fixed Task.Delay(proofWindow) presentation gate with an event-driven wait on HasReportStream property change;
• retain the bounded proof window only as a timeout/diagnostic boundary, not as a polling mechanism or activation prerequisite;
• log observed first-report latency when traffic arrives;
• correct static-report-only reconnect diagnostics so they never claim MMS polling resumed when process polling is intentionally disabled.

Safety

• no change to ARIEC RCB/DataSet activation semantics;
• no vendor branching;
• no process-value heartbeat is introduced;
• no polling fallback is introduced for Static DataSet report-only mode;
• absence of report traffic within the diagnostic window remains armed/report-pending, not an activation failure;
• reconnect cleanup remains bounded by the existing SmartReconnectPolicy.ClientCleanupBudget.

Regression

Adds P7.2 guards proving:

• no Ping/ICMP authoritative liveness or second UI reconnect owner remains;
• report traffic proof is cleared on offline + replacement-association boundaries;
• static traffic proof is event-driven and has no fixed Task.Delay(proofWindow);
• Static DataSet reconnect diagnostics preserve the no-polling invariant.

Physical retest is still required after software CI.