poc-daemon: fix pane tracking, suppress notifications when user present

Three fixes:

- Persist claude_pane via thalamus extra map so it survives every
  save path (not just explicit Save commands)
- Don't clobber claude_pane with empty string when TMUX_PANE is unset
- signal_response now passes TMUX_PANE like signal_user does
- maybe_prompt_notification returns early when user is present,
  preventing notification spam during active sessions

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/poc-hook.rs

@@ -66,7 +66,12 @@ fn signal_user() {
 }
 
 fn signal_response() {
-    daemon_cmd(&["response"]);
+    let pane = std::env::var("TMUX_PANE").unwrap_or_default();
+    if pane.is_empty() {
+        daemon_cmd(&["response"]);
+    } else {
+        daemon_cmd(&["response", &pane]);
+    }
 }
 
 fn check_notifications() {