Harden keybinding schemas and align tests with server defaults

- make resolved keybinding/shortcut schemas strict to reject unknown fields
- export server `DEFAULT_KEYBINDINGS` as source of truth and reuse it in ws tests
- simplify keybinding test fixtures and update docs to reference server defaults
b8dfe54154Julius Marminge committed on 2/15/2026, 10:20:50 PMparente1660c6
6 files changedLine totals unavailable