feat(config): show default keybindings in generated example config (#64)

- Expand `keybindings` array in `config.example.jsonc` to list all built-in defaults instead of `[]`
- Inject `DEFAULT_KEYBINDINGS` into template when resolved config has an empty keybindings array
- Add regression tests for template parity, default binding compile/action mapping, overlay keyboard dispatch, and mpv plugin registration/dispatch
- Add fullscreen binding to docs shortcut tables and clarify keybindings can target mpv commands or session actions

src/config/definitions/template-sections.ts

@@ -62,7 +62,7 @@ const CORE_TEMPLATE_SECTIONS: ConfigTemplateSection[] = [
   {
     title: 'Keybindings (MPV Commands)',
     description: [
-      'Extra keybindings that are merged with built-in defaults.',
+      'Default and custom keybindings that are merged with built-in defaults.',
       'Set command to null to disable a default keybinding.',
     ],
     notes: [