refactor composer to use sqlalchemy, avoid string concatenations and follow conventions

ui/app/src/pages/Ask.vue

@@ -141,7 +141,6 @@ function nodeClasses(n: GraphNode) {
     <div class="trace-pane">
       <Panel title="Plan" :status="statusOf(status)">
         <div v-if="rationale" class="rationale">{{ rationale }}</div>
-        <div v-else class="muted small">Waiting for the planner…</div>
 
         <div class="graph">
           <div v-for="(n, idx) in graphNodes" :key="n.id" class="graph-row">