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/Planning/PlanningSessionContext.cs

@@ -5,11 +5,6 @@ public sealed record PlanningSessionFiles(
     string SystemPromptPath,
     string InitialPromptPath);
 
-public sealed record InteractiveLaunchContext(
-    string TaskId,
-    string WorkingDir,
-    string InitialPrompt);
-
 public sealed class PlanningMcpContext
 {
     public required string ParentTaskId { get; init; }