feat: add navigation actions to the waffle menu

[susnux]

• resolves App navigation: file creation actions in waffle menu #59951
• resolves App Navigation Redesign #59888

Summary

Tip

For testing best to use the example implementation here: nextcloud/calendar#8714

This implements navigation action similar to navigation entries, but they have a dedicated section in the waffle menu with an overflow menu. Actions allow either a link or the more interesting in-app action.
If no link is supplied the action will trigger an event on the event bus (core:navigation:action) with the action object as the payload.
This allows apps to listen and handle such events and then render e.g. a dialog to create an event or do what ever action they registered (see the linked example for creating events above).

This also fixes some issues unrelated in the app menu:

• On narrow screens the height of the waffle menu was not limited - this is fixed now
• Once the menu was clamped the actual row height was invalid causing overflow of app navigation labels

Action flow

Bildschirmaufnahme_20260810_222403.webm

Screenshots

Normal waffle

Overflow menu

No overflow menu needed

Narrow screen

No actions registered

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI