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/events/bus.dart

@@ -2,8 +2,8 @@ import 'dart:async';
 
 import 'package:clide/kernel/src/events/types.dart';
 
-class EventBus {
-  EventBus();
+class DaemonBus {
+  DaemonBus();
 
   final StreamController<ClideEventEnvelope> _controller =
       StreamController<ClideEventEnvelope>.broadcast();

lib/kernel/src/events/message_bus.dart

@@ -0,0 +1,36 @@
+import 'dart:async';
+
+class Message {
+  Message({
+    required this.publisher,
+    required this.channel,
+    required this.data,
+  }) : timestamp = DateTime.now();
+
+  final String publisher;
+  final String channel;
+  final DateTime timestamp;
+  final Map<String, Object?> data;
+
+  String get address => '$publisher/$channel';
+}
+
+class MessageBus {
+  final _controller = StreamController<Message>.broadcast();
+
+  void publish(String publisher, String channel, Map<String, Object?> data) {
+    _controller.add(Message(publisher: publisher, channel: channel, data: data));
+  }
+
+  Stream<Message> subscribe({String? publisher, String? channel}) {
+    return _controller.stream.where((m) {
+      if (publisher != null && m.publisher != publisher) return false;
+      if (channel != null && m.channel != channel) return false;
+      return true;
+    });
+  }
+
+  void dispose() {
+    _controller.close();
+  }
+}