fix: correct misleading send_message tool description for scheduled tasks (#729)

The send_message tool description incorrectly stated that a scheduled
task's final output is not delivered to the user, instructing agents to
use the MCP tool for any communication. In reality, task-scheduler.ts
unconditionally forwards the agent's result to the user via a streaming
output callback (deps.sendMessage), which is a direct call to the
channel layer — entirely separate from the MCP tool path.

This caused agents following the description to call send_message
explicitly, resulting in duplicate messages: once via MCP and once via
the native streaming callback.

- Remove the incorrect note from the send_message tool description
- Fix the misleading comment at task-scheduler.ts which attributed
  result delivery to the MCP tool rather than the streaming callback

src/task-scheduler.ts

@@ -203,7 +203,7 @@ async function runTask(
     if (output.status === 'error') {
       error = output.error || 'Unknown error';
     } else if (output.result) {
-      // Messages are sent via MCP tool (IPC), result text is just logged
+      // Result was already forwarded to the user via the streaming callback above
       result = output.result;
     }