web: export menu, slice 11 of M3

The toolbar's Export button becomes a real menu: Data (JSON) downloads
{ base, panels, results } exactly as held in the store, Per-node CSV
writes one row per panel and node (educated flag, reachedAtRound with
-1 kept), and Picture (PNG) rasterizes each panel's live SVG with the
current theme's token values resolved, drawn side by side with labels
and the live percentage at the current round, plus legend and the
disclaimer footer line, at 2x. Items disable while a run is in flight
so exports always capture settled state.

web/src/components/ExportMenu.vue

@@ -0,0 +1,111 @@
+<script setup lang="ts">
+import { computed, ref } from 'vue'
+import PanelMenu, { type PanelMenuItem } from './PanelMenu.vue'
+import { useSimStore } from '@/composables/useSimStore'
+import { exportCsv, exportJson, exportPng } from '@/lib/export'
+
+// The toolbar's Export dropdown (spec 5.9). Items disable while a run is
+// in flight so an export always captures settled state.
+
+const store = useSimStore()
+
+const open = ref(false)
+const exporting = ref(false)
+const button = ref<HTMLButtonElement | null>(null)
+
+const busy = computed(
+  () =>
+    store.state.runState === 'running' ||
+    exporting.value ||
+    Object.keys(store.state.resultsByPanelId).length === 0,
+)
+
+const items = computed<PanelMenuItem[]>(() => [
+  { key: 'json', label: 'Data (JSON)', disabled: busy.value },
+  { key: 'csv', label: 'Per-node CSV', disabled: busy.value },
+  { key: 'png', label: 'Picture (PNG)', disabled: busy.value },
+])
+
+async function onSelect(itemKey: string) {
+  open.value = false
+  button.value?.focus()
+  if (busy.value) return
+  if (itemKey === 'json') {
+    exportJson(store)
+  } else if (itemKey === 'csv') {
+    exportCsv(store)
+  } else if (itemKey === 'png') {
+    exporting.value = true
+    try {
+      await exportPng(store)
+    } finally {
+      exporting.value = false
+    }
+  }
+}
+
+function closeMenu() {
+  open.value = false
+  button.value?.focus()
+}
+</script>
+
+<template>
+  <span class="anchor">
+    <button
+      ref="button"
+      class="btn"
+      type="button"
+      aria-haspopup="menu"
+      :aria-expanded="open"
+      aria-label="Export"
+      @click="open = !open"
+    >
+      <svg class="ic" viewBox="0 0 24 24"><path d="M12 4v11m0 0l-4-4m4 4l4-4M5 20h14" /></svg>
+      <span class="btn-text">Export</span>
+    </button>
+    <PanelMenu v-if="open" :items="items" :anchor="button" @select="onSelect" @close="closeMenu" />
+  </span>
+</template>
+
+<style scoped>
+.anchor {
+  position: relative;
+  display: inline-flex;
+}
+
+.btn {
+  display: inline-flex;
+  align-items: center;
+  gap: 7px;
+  font-size: 13.5px;
+  font-weight: 600;
+  line-height: 1;
+  color: var(--ink-2);
+  background: var(--surface);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  padding: 8px 14px;
+  cursor: pointer;
+  box-shadow: 0 1px 2px rgba(15, 23, 42, 0.04);
+}
+
+.btn:hover {
+  border-color: var(--ink-4);
+}
+
+.btn svg.ic {
+  width: 15px;
+  height: 15px;
+}
+
+@media (max-width: 760px) {
+  .btn {
+    min-height: 44px;
+  }
+
+  .btn-text {
+    display: none;
+  }
+}
+</style>