add pane subsystem to the daemon + IPC event broadcast

Implements the Tier-1 pane subsystem from D-006: spawn / list / focus /
close / write / resize / tail commands, plus pane.spawned / output /
exit / resized / focused / closed events. PaneRegistry owns per-pane
PtySession lifecycles and id generation (p_N); a DaemonEventSink seam
keeps pane code decoupled from the IPC server package.

DaemonServer.broadcast() fans events out to every connected client.
Per-client subsystem/id filtering (`tail --filter pane:p_7`) is
deferred — Tier 1 broadcasts everything and the subscriber discards.

Panes carry a `kind:` field (terminal | claude). Step 7 (builtin.claude)
adds the claude-specific pane flow on top of this generic substrate —
the subsystem itself stays neutral.

14 new core tests: registry unit coverage (spawn → pane.spawned event,
output → base64 events, write/resize/close round-trips, idempotent
close, claude kind on the wire) plus dispatcher coverage (argv
validation, unknown-id → not-found, text vs bytes_b64, etc). All 37
core tests pass in ~3s under test-core.

Co-Authored-By: Claude <noreply@anthropic.com>

bin/clide.dart

@@ -67,10 +67,13 @@ Matches ADR 0006's exit-code contract:
 Future<void> _runDaemon(List<String> args) async {
   final socketPath = defaultSocketPath();
   final dispatcher = DaemonDispatcher();
-  final server = DaemonServer(
+  late final DaemonServer server;
+  server = DaemonServer(
     socketPath: socketPath,
     dispatch: dispatcher.dispatch,
   );
+  final registry = PaneRegistry(events: _ServerEventSink(server));
+  registerPaneCommands(dispatcher, registry);
 
   final stopping = Completer<void>();
   void shutdown(ProcessSignal sig) {
@@ -85,10 +88,22 @@ Future<void> _runDaemon(List<String> args) async {
 
   await server.start();
   await stopping.future;
+  await registry.shutdown();
   await server.stop();
   exit(0);
 }
 
+/// Thin adapter: the server doesn't `implement DaemonEventSink` itself
+/// (that would tie ipc/ to panes/); instead the daemon entrypoint wraps
+/// it at the seam where both are known.
+class _ServerEventSink implements DaemonEventSink {
+  _ServerEventSink(this._server);
+  final DaemonServer _server;
+
+  @override
+  void emit(IpcEvent event) => _server.broadcast(event);
+}
+
 Future<void> _runCli(
   String cmd,
   List<String> args, {