* Align MCP provider controls with app provider state
* Deepen provider snapshot routing
* Make provider snapshots the daemon authority
* Move provider shutdown behind a generic AgentClient seam
OpenCodeServerManager is now owned entirely by the OpenCode provider.
ProviderSnapshotManager.shutdown() and provider-registry.shutdownProviders()
materialize enabled clients and call an optional shutdown() per client; the
OpenCode client forwards to its runtime. Other providers ignore it.
Also wires providerSnapshotManager into the remaining Session-constructing
tests that were missing it (server-tests CI failure).
* Use platform-native cwd in change-event test
