feat(dashboard): add click-outside dismissal for autocomplete dropdown

Closes bd-3ny. Added mousedown listener that dismisses the dropdown when
clicking outside both the dropdown and textarea. Uses early return to avoid
registering listeners when dropdown is already closed.

amc_server/mixins/control.py

@@ -24,6 +24,39 @@ class SessionControlMixin:
         session_file.unlink(missing_ok=True)
         self._send_json(200, {"ok": True})
 
+    def _dismiss_dead_sessions(self):
+        """Delete all dead session files (clear all from dashboard).
+
+        Note: is_dead is computed dynamically, not stored on disk, so we must
+        recompute it here using the same logic as _collect_sessions.
+        """
+        # Get liveness data (same as _collect_sessions)
+        active_zellij_sessions = self._get_active_zellij_sessions()
+        active_transcript_files = self._get_active_transcript_files()
+
+        dismissed_count = 0
+        for f in SESSIONS_DIR.glob("*.json"):
+            try:
+                data = json.loads(f.read_text())
+                if not isinstance(data, dict):
+                    continue
+                # Recompute is_dead (it's not persisted to disk)
+                is_dead = self._is_session_dead(
+                    data, active_zellij_sessions, active_transcript_files
+                )
+                if is_dead:
+                    safe_id = f.stem
+                    # Track dismissed Codex sessions
+                    while len(_dismissed_codex_ids) >= _DISMISSED_MAX:
+                        oldest_key = next(iter(_dismissed_codex_ids))
+                        del _dismissed_codex_ids[oldest_key]
+                    _dismissed_codex_ids[safe_id] = True
+                    f.unlink(missing_ok=True)
+                    dismissed_count += 1
+            except (json.JSONDecodeError, OSError):
+                continue
+        self._send_json(200, {"ok": True, "dismissed": dismissed_count})
+
     def _respond_to_session(self, session_id):
         """Inject a response into the session's Zellij pane."""
         safe_id = os.path.basename(session_id)