fix(ui): companion rail loads current space on initial page load

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

public/app.js

@@ -35,6 +35,10 @@ async function renderView(ctx) {
   } else {
     state.view = null;
   }
+  // Notify subscribers (right rail) of the active Space. The state bus replays
+  // the last value on subscribe, so this covers both the initial route() call
+  // and every subsequent navigation with one path.
+  emit('space-active', state.spaceId);
 
   const main = document.getElementById('main');
   const loader = VIEWS[ctx.name] || VIEWS.home;