Feature request: Co-op puzzle session for coach & student

[ilia-pavlov]

Summary

A shared puzzle session where a coach and student solve the same
puzzle simultaneously and can see each other's moves in real
time.

Use case

Currently coaches can review games and annotate studies, but
there's no way to work through tactics together live. A co-op
puzzle mode would let a coach guide a student through tactical
patterns interactively — the student attempts the puzzle, the
coach watches and can highlight squares or suggest moves, both
seeing the same board.

Proposed behaviour

• Coach creates a session and shares a link with the student
• Both land on the same puzzle
• Each player's moves/clicks are visible to the other (similar to
  how study boards work)
• Coach can optionally "reveal" the solution or nudge the student
  with an arrow
• Session can move through a sequence of puzzles together

Why Lichess is well-positioned for this

The WebSocket infrastructure, puzzle engine, coach/student
relationships, and study board already exist — this would combine
them in a new mode.

[johndoknjas]

As a coach I think something like this would be great.

[yafred]

Would it help if the coach was able to create a study chapter from the puzzle ?

Either with a button 'create study' or a button 'get position (FEN)'