👑 feat(owners): Allow to promote/demote users to/from owners

[nickvergessen]

☑️ Resolves

• Related to feat(conversations): Allow to preserve conversations (restrict deletion, purging, public link and listable change) #18351

Decisions:

• Only owners can promote to owners
• Owners are not mandatory, only 1 moderator remains mandatory
• Self-demotion to moderator is allowed
• Removing owners directly is not possible, it's needed to demote them first

AI (if applicable)

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

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

User (with extended permissions)	Moderator	Owner	Participant list

🚧 Tasks

• Discuss final icons with @nimishavijay

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Integrations with Files sidebar and other apps
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

🛠️ API Checklist

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not possible
• 📘 API documentation in docs/ has been updated or is not required
• 🔖 Capability is added or not needed

[jancborchardt]

Sounds good, but the wording would be better as "participant" instead of "user" as we use that in the tab header already.

And the 2 titles in src/components/RightSidebar/Participants/ParticipantItem.vue should probably start with a capital letter. It looked fine lowercase when they were in parentheses behind the username, but in a standalone title it looks better properly cased.

[Antreesy]

Addressed design commits, checked
From frontend side - good to go