Clear terminal attention when the user views the terminal

A finished or input-waiting terminal shows an attention indicator. The
focus heartbeat already asked the daemon to clear it, but the clear was a
no-op: it guarded on activity state === "attention", while the real
tracker encodes attention as state "idle" plus an attentionReason
("finished" / "needs_input"). The state is never literally "attention",
so the indicator only ever cleared when the agent started a new turn.

The worker proxy also had no way to reach the tracker's clearAttention():
it only spoke setActivity, and setActivity("idle") is short-circuited by
the tracker while a "finished" reason is set. Add a clearAttention worker
message that calls the existing manager.clearTerminalAttention(), and
guard both clear paths on attentionReason instead of state.

packages/server/src/terminal/terminal-worker-process.ts

@@ -258,6 +258,12 @@ async function handleRequest(message: TerminalWorkerRequest): Promise<void> {
       return;
     }
 
+    case "clearAttention": {
+      await manager.clearTerminalAttention(message.terminalId);
+      sendToParent({ type: "response", requestId: message.requestId, ok: true });
+      return;
+    }
+
     case "killTerminal": {
       const session = manager.getTerminal(message.terminalId);
       const cwd = session?.cwd;