Make y.js connection status to yjs server visible in tiptap UI #3109

Initial Checklist

• I understand this is a user story and questions should be posted in the Community Discussions
• I searched issues and couldn’t find anything (or linked relevant results below)

User Story

As a user, I want to see whether I am connected to the y.js server so that I know whether my changes are being shared with the others in the session.

User Value

UX, trust

Acceptance Criteria

• The editor shows the connection state: connected, connecting/reconnecting, disconnected
• While disconnected, the user is told that changes stay local and may conflict on save
• The indicator updates automatically once the connection recovers
• The state is not conveyed by colour alone (label/tooltip, accessible to screen readers)
• No indicator is shown for files that are not collaborative (e.g. vault files, collaboration disabled)