feat(console): toolbar toggle to hide per-line color accent bars

Adds a paint-bucket toggle button to the console toolbar (in the appearance
cluster next to zoom) that shows/hides the per-line left color accent bars for
a cleaner monochrome gutter. The icon reflects state (FORMAT_COLOR_FILL when on,
a dimmed FORMAT_COLOR_RESET when off) with a tooltip. Session-only, like the
console zoom factor; default on.

Adds console_toggle_accents to the English source and all eight translations
(no new CJK glyphs — the subset font already covers them).

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

src/util/i18n.cpp

@@ -1290,6 +1290,7 @@ void I18n::loadBuiltinEnglish()
         strings_["console_welcome"] = "Welcome to ObsidianDragon Console";
         strings_["console_zoom_in"] = "Zoom in";
         strings_["console_zoom_out"] = "Zoom out";
+        strings_["console_toggle_accents"] = "Toggle line color accents";
 
         // --- Export All Keys Dialog ---
         strings_["export_keys_btn"] = "Export Keys";