billboard applets: single-root wrapper for HTMX swap; full context on toggle — TDD

- _applets.html wraps menu + container in one #id_billboard_applets_wrapper div; form's hx-target is now the wrapper, so OK no longer leaves a stale duplicate menu in the DOM (which previously caused the next OK to revert prior toggles)
- toggle_billboard_applets passes full context (recent_room, recent_events, viewer, my_rooms) via factored _billboard_context helper, so Most Recent + My Scrolls keep their content after a toggle instead of falling through to the empty fallback
- applets.js: register id_billboard_applets_wrapper as an applet container so post-swap menu cleanup runs
- BillboardAppletsTest: portrait viewport in setUp; FT covers content preservation, no-revert on second toggle, & post-refresh state
- 4 new ITs: Most Recent renders Coin-on-a-String after toggle; My Scrolls renders room name; response has single menu div; second toggle preserves prior hidden state

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/apps/applets/static/apps/applets/applets.js

@@ -30,6 +30,7 @@ const appletContainerIds = new Set([
     'id_game_applets_container',
     'id_gk_sections_container',
     'id_wallet_applets_container',
+    'id_billboard_applets_wrapper',
 ]);
 
 document.body.addEventListener('htmx:afterSwap', (e) => {