Add keyboard shortcuts cheatsheet to desktop match UI

[MostCromulent]

Summary

• Adds a keyboard shortcuts cheatsheet to the desktop UI, accessible via configurable key (default "H" for "Hotkeys") during matches and from Help > Keyboard Shortcuts in the menu bar.
• Configurable shortcuts are shown with in-place rebinding (click a field, press a new key to replace the binding)
• Configurable shortcuts auto-populate by iterating KeyboardShortcuts.getCachedShortcuts(), so if a new SHORTCUT_* FPref entry is added to Forge in future it will automatically appear in the dialog without needing changes to the dialog code.
• Hard coded shortcuts (F1, F11, Ctrl+Z, Ctrl+Q, Ctrl+A, Ctrl+E, Ctrl+T, Ctrl+O) are hardcoded in the dialog because they are defined across separate menu classes (GameMenu, LayoutMenu, CardOverlaysMenu, HelpMenu) with no shared registry, so there is no list to iterate.

^{(Note: In images above Concede, Alpha Strike, and End Turn appear in both sections. That is because they currently exist as both configurable shortcuts (though default for concede is non-functional — assembleKeystrokes treats CTRL as modifier rather than key press). The fixed Ctrl+Q/A/E menu accelerators are separate bindings tied to the menu bar items. Both systems trigger the same game actions. This is existing Forge behavior, not anything added in this PR - while outside scope of this PR, it may be worth streamlining this in future.)}

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