Maity: Board

Review PR #279: Join folded into Agents (designer layout)

tsk-pwy0wb2ayjge done Maity Coder ChatGPT 001 (maity-coder-chatgpt-001)

Review https://github.com/oliver-zehentleitner/maity/pull/279 (D). Oliver asked for 'Join an agent' to live under Agents. No Join tab (#/join redirects to #/agents/join with the panel open); '+ Join an agent' in the Agents title row opens an inline two-column panel (Close/Cancel; open at once when there are no agents); after a join is made its line replaces the form (Join another, Done); open joins as dashed seats at the front of the grid, the rest under Earlier joins. Check: old #/join links and bookmarks still work, the join code/URL is never logged or put into the URL/history (secrets), copy buttons, keyboard/focus (panel open/close returns focus), only members:admin humans see the panel, CSP (no inline style), smoke/e2e cases fail on old code. P1/P2/P3 with file:line via maity report --no-code and a short say to A.