feat(worker): in-app interactive session service, replacing the wt terminal launch

InteractiveSessionService resolves a task's list working dir + seeded prompt,
spawns a StreamingClaudeSession (claude stream-json in the list dir, model+auto
as before), registers it in LiveSessionRegistry, streams output over TaskMessage,
and broadcasts InteractiveSessionStarted/Ended (an exit watcher fires Ended). The
hub's OpenInteractiveTerminalAsync now starts this in-app session; SendInteractiveMessage
and StopInteractiveSession route to it. The external Windows-Terminal interactive
launch (LaunchInteractiveAsync / InteractiveLaunchContext / OpenInteractiveAsync) is
removed; planning sessions keep their terminal launch.

src/ClaudeDo.Worker/Program.cs

@@ -80,6 +80,8 @@ builder.Services.AddSingleton<TaskMergeService>();
 builder.Services.AddSingleton<PlanningAggregator>();
 builder.Services.AddSingleton<PlanningMergeOrchestrator>();
 builder.Services.AddSingleton<PlanningChainCoordinator>();
+builder.Services.AddSingleton<LiveSessionRegistry>();
+builder.Services.AddSingleton<InteractiveSessionService>();
 
 // Queue dispatch primitives. QueueWaker holds the wake semaphore; the queue picker
 // performs atomic Queued→Running claim. Both injected into the state service so it