feat: support checkbox type for extension preferences

[flash7777]

Summary

Extension points can now declare userPreference.type: 'checkbox' to render a checkbox toggle instead of a dropdown select on the account Extensions preferences page.

Motivation

Web extensions that need simple boolean user settings (e.g. "Show Aktenzeichen in folder names") currently have no way to add a toggle to the preferences UI. The only option is a dropdown select, which is awkward for on/off settings.

Changes

File	Change
types.ts	Add optional type?: 'select' | 'checkbox' to ExtensionPoint.userPreference
ExtensionPreference.vue	Render oc-checkbox when type === 'checkbox', existing select behavior unchanged

Usage

// In extension setup:
const extensionPoint = {
  id: 'com.example.my-toggle',
  extensionType: 'customComponent',
  userPreference: {
    label: 'Show extra info',
    description: 'Display additional metadata in folder names',
    type: 'checkbox'
  }
}

For checkbox mode, register two extensions on the point — first = checked state, second = unchecked state. Default type is 'select' (backward compatible).

Test plan

• Existing select-based extension preferences still work unchanged
• New checkbox preference renders as toggle on Extensions page
• Checkbox state persists via extensionPreferencesStore