fix(worker): reap idle interactive sessions so they don't pile up

Interactive/streaming sessions are persistent claude.exe processes that
wait on stdin and never exit on their own. The only teardown was an
explicit StopInteractiveSession from the UI — there is no client-disconnect
or shutdown sweep — so an abandoned chat (UI closed, navigated away,
crashed) kept its claude.exe (+ conhost) alive for the worker's whole
lifetime. Under a long-running autostart worker these accumulate to dozens
of orphaned child processes.

LiveSessionRegistry now tracks per-session activity (Touch on every output
line and user action) and exposes ReapIdleAsync, which stops sessions idle
past a timeout while skipping any with a turn in flight. IdleSessionReaper
(BackgroundService) sweeps every 5 min; idle timeout defaults to 30 min,
configurable via interactive_idle_timeout_minutes (0 disables).

src/ClaudeDo.Worker/Config/WorkerConfig.cs

@@ -41,6 +41,10 @@ public sealed class WorkerConfig
     [JsonPropertyName("external_mcp_api_key")]
     public string? ExternalMcpApiKey { get; set; }
 
+    /// <summary>Interactive/streaming sessions idle longer than this are stopped by IdleSessionReaper. 0 disables reaping.</summary>
+    [JsonPropertyName("interactive_idle_timeout_minutes")]
+    public int InteractiveIdleTimeoutMinutes { get; set; } = 30;
+
     [JsonPropertyName("online_inbox")]
     public OnlineInboxConfig OnlineInbox { get; set; } = new();