Add multiplayer click button

[rayzhudev]

Summary

• Add a Click button to the hosted multiplayer browser page
• Send a participant chat message with text click when the button is pressed
• Disable browser buttons until the websocket connection is open

Tests

• just fmt
• cargo test -p codex-tui multiplayer_page_includes_click_button
• cargo test -p codex-tui (fails: stack overflow in app::tests::attach_live_thread_for_selection_rejects_unmaterialized_fallback_threads)
• just fix -p codex-tui (fails: no space left on device while compiling aws-lc-sys)