add image-viewer card + clide image show verb

Drives an image inline into the Claude conversation log over the same
bus-publish path as ui.toast/ui.open, keeping the dispatcher handler
Flutter-free. The card is display-only per D-78; the verb registers a
CommandSchema so it surfaces in clide capabilities for T-248 discovery.

Closes T-249.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/claude/src/conversation_controller.dart

@@ -71,6 +71,15 @@ class ConversationController extends ChangeNotifier {
 
   bool get isEmpty => _items.isEmpty;
 
+  /// Append a locally-produced item that did not come from the transcript
+  /// stream — e.g. an image card driven by `clide image show` (T-249). It
+  /// lands in arrival order and notifies listeners exactly like a streamed
+  /// item, so the view renders it inline. No-op once disposed.
+  void inject(ConversationItem item) {
+    if (_disposed) return;
+    _onItem(item);
+  }
+
   void _onItem(ConversationItem item) {
     // Track AssistantToolUse items by toolUseId for result-card pairing (T-168).
     if (item is AssistantToolUse) {