Allow remapping/disabling GUI menu keyboard shortcuts (View menu, etc.)

Currently, `~/.claude/keybindings.json` only customizes shortcuts for the terminal/interactive CLI. The desktop app's native GUI menu shortcuts (File/Edit/View/Move menus — e.g. サイドチャット(Side Chat)=Ctrl+;, ターミナル(Terminal)=Ctrl+`, 変更(Changes)=Ctrl+Shift+D, ブラウザ(Browser)=Ctrl+Shift+B, ファイル(Files)=Ctrl+Shift+F, ペインを閉じる(Close Pane)=Ctrl+¥, etc.) are hardcoded and cannot currently be remapped or disabled through any in-app settings screen or config file.

This becomes a real problem when a hardcoded menu shortcut collides with another application's global shortcut — for example, IME (Japanese input method) candidate-selection shortcuts often use Ctrl+; which collides with the "サイドチャット" (Side Chat) menu item. IME shortcuts are shared across all applications on the system, so it isn't reasonable to ask users to change their IME configuration just to avoid a conflict with one app's hardcoded menu shortcut.

**Request**: please add a way to customize (remap or disable) the desktop app's native GUI menu shortcuts — ideally by extending `~/.claude/keybindings.json` to also cover these menu-level bindings, or via an in-app Settings screen.

Start with ~/.claude/keybindings.json and trace how the desktop app defines its native File, Edit, View, and Move menu shortcuts. Determine how remapping and disabling should be represented, then verify that the listed menu shortcuts can be customized without colliding with external shortcuts such as Japanese IME bindings.

Written by the indexing model from the issue text.