split EventBus into DaemonBus + MessageBus

DaemonBus (was EventBus): typed events for system/IPC layer.
MessageBus: channel-based pub/sub for UI/extension coordination.
Messages carry publisher (auto-stamped from extension ID),
channel (required), timestamp, and payload. Subscribe by
publisher, channel, or both — zero collision across extensions.

Extension context gains publish() and subscribe() convenience
methods that auto-stamp the extension's ID as publisher.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/kernel/src/ipc/client.dart

@@ -13,13 +13,13 @@ class DaemonClient extends ChangeNotifier {
   DaemonClient({
     required this.socketPath,
     required Logger log,
-    required EventBus events,
+    required DaemonBus events,
   })  : _log = log,
         _events = events;
 
   final String socketPath;
   final Logger _log;
-  final EventBus _events;
+  final DaemonBus _events;
 
   Socket? _socket;
   bool _connected = false;

lib/kernel/src/ipc/in_process.dart

@@ -7,7 +7,7 @@ import 'package:clide/src/daemon/dispatcher.dart';
 class InProcessClient extends DaemonClient {
   InProcessClient({
     required Logger log,
-    required EventBus events,
+    required DaemonBus events,
     required this.dispatcher,
   }) : super(socketPath: '', log: log, events: events);