Add global hotkey (shortcuts) management

• ref: https://github.com/nextcloud-libraries/nextcloud-vue/pull/6311/
• ref: https://github.com/nextcloud/server/issues/30484

Problem

Currently, we have hotkeys (shortcuts) in many apps and components. It includes:

1. Setting the global hotkey listener taking into account a11y, macOS, and focus
2. Showing the keymap

While setting the hotkey listener is covered by useHotkey, showing "Keyboard shortcuts" is implemented manually by apps.

Files	Talk

It results in the following problems:

• Each app must implement the settings section again
• Each app should include global shortcuts like new n</kbd< for App Navigation toggle
• Consistency and relevance:
  • Design consistency
  • Open dialog by ? (not implemented by Talk)
  • macOS - Ctrl is replaced with Cmd on macOS (not implemented by Files)
  • Manual update - after adding the hotkey developers should not forget to add it to the docs (especially with global hotkeys)

Proposal

Add a global shortcut manager together with useHotkey

1. When registering a hotkey, allow defining:
   • Description, e.g. Select all files
   • Section, e.g. Actions
   • App (can be defined automatically from NcContent), e.g. Files or Global for all-apps
2. Store the fact of hotkey registration globally in window
3. Add components <NcHotkeys> and <NcHotkeysDialog> with the list of hotkeys and ?

Implementation notes

We might use useHotkey to handle the fact of (un)registration. But some hotkeys are registered only in a specific context like a call in Talk. So we don't know about a hotkey in advance.

Instead, we can add an app-level composable like

declare function useAppHotkey(options: { id: string, key: string, description: string, section?: string })

useAppHotkey()

Then useHotkey should refer to a registered app hotkey (via id or a new composable wrapper).

Vue

Implementing it as a composable allows automatic unregistration and useHotkey integration.

But the functionality might make sense even without Vue. Maybe it should be also available outside composables and the vue library.

Start by reading the existing useHotkey composable and the NcContent integration mentioned in the proposal. Trace how hotkeys register and unregister, including context-specific Talk shortcuts. Done should include the proposed global registration, NcHotkeys and NcHotkeysDialog components, and the ? shortcut, with the API boundaries resolved for use outside Vue.