Dock: floating windows hold one pallet again

Remove floating groups: a floating window is a single pallet once more,
and the Pallets submenu is gone from its title-bar menu. Kept: the menu
opens at the pointer with Allow docking, Dock left and Dock right;
close / pin show only while the bar is hovered; content is clipped to
its frame. A config saved by the floating-group build still loads, its
windows floating their first pallet. Drops the unused Pallets string.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013RyGiMXcsf9HTKfqDxaQGt

locales/ru-RU/opencadstudio.ftl

@@ -6160,6 +6160,5 @@ dock =
     .dock-left = Закрепить слева
     .dock-right = Закрепить справа
     .new-group = Новая группа
-    .pallets = Палитры
     .browser = Обозреватель
     .node-graph = Граф узлов