fix: disable furigana when switching to DNCL mode

When switching directly from furigana mode to DNCL mode, furigana
annotations were not cleared because handleSelectDnclMode did not
disable furigana. DNCL mode uses Japanese text, so furigana is
redundant and should always be turned off.

Fixes #514

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

Author: takaokouji

packages/scratch-gui/src/components/ruby-toolbar/ruby-toolbar.jsx

@@ -86,8 +86,9 @@ const RubyToolbar = props => {
 
     const handleSelectDnclMode = useCallback(() => {
         if (props.onDismissBubble) props.onDismissBubble();
-        // Switch to DNCL mode
+        // Switch to DNCL mode (disable furigana since DNCL is already in Japanese)
         if (!props.dnclMode && props.onToggleDnclMode) props.onToggleDnclMode();
+        if (props.furiganaEnabled && props.onToggleFurigana) props.onToggleFurigana();
     }, [props]);
     // === Smalruby: End of mode selection handlers ===