ADR-013 Phase 4: frontend staging machinery + relocate printedparts; fix router crash

The staging step that makes lean per-site frontend builds possible, plus the
first plugin relocated as the pilot.

- scripts/stage-frontend.mjs: copies each chosen plugin's plugins/<name>/frontend/
  into frontend/src/.plugins-staged/<name>/ and codegens routes.gen.js. Plugin
  selection via SITE_PLUGINS (comma-separated); empty = all plugins that have a
  frontend/ (the full build). Wired as npm predev/prebuild; outputs gitignored.
- Router imports routes.gen.js and merges staged routes with the in-tree
  ./routes/*.js glob - dual-location during the transition.
- printedparts relocated: its 6 views (list/detail/form/kiosk + the settings and
  labels views from the shared dirs) moved into plugins/printedparts/frontend/
  views/, core imports rewritten to the @/ alias; routes.js is the self-contained
  route module. Its old in-tree route file is removed.

Also fixes a crash the previous commit (37c764b) shipped: slides.js exports only
`toplevel` (its child routes live in core.js), so the router's
flatMap(m => m.default) produced an undefined child and threw
"Cannot read properties of undefined (reading 'path')" at load - the whole SPA
went blank. Guarded with `m.default || []`. (The earlier "print pages are blank"
reading was this crash, not page nature.)

Verified live: /machines renders again; the relocated /printedparts list renders
identically from the staged plugin frontend; SITE_PLUGINS=machines excludes
printedparts from routes.gen. Build (via npm, runs stage) + vitest + naming green.

plugins/printedparts/frontend/views/PrintedPartsLabels.vue

@@ -0,0 +1,207 @@
+<template>
+  <div>
+    <div class="no-print">
+      <div class="controls">
+        <h3>Print 3D Parts Bin Labels (1in x 0.5in)</h3>
+        <p>
+          Each label is one page on 1in x 0.5in roll stock: CODE128 barcode of
+          the item code, scannable at the parts kiosk.
+        </p>
+
+        <div v-if="loading" class="loading-msg">Loading parts...</div>
+        <div v-else-if="items.length === 0" class="loading-msg">No parts found</div>
+        <div v-else class="parts-grid">
+          <div
+            v-for="item in items"
+            :key="item.printeditemid"
+            class="part-item"
+            :class="{ selected: isSelected(item) }"
+            @click="toggleItem(item)"
+          >
+            <input type="checkbox" :checked="isSelected(item)" @click.stop />
+            <label>
+              <strong><code>{{ item.itemcode }}</code></strong>
+              <div class="alias">{{ item.itemname }}</div>
+            </label>
+          </div>
+        </div>
+
+        <div class="selected-count">
+          Selected: <span class="count">{{ selectedItems.length }}</span> labels
+          <label class="copies-label">Copies each:
+            <input v-model.number="copies" type="number" min="1" max="10" />
+          </label>
+        </div>
+
+        <button class="print-btn" :disabled="selectedItems.length === 0"
+                @click="print">Print Labels</button>
+        <button class="clear-btn" @click="selectedItems = []">Clear All</button>
+        <button class="select-all-btn" @click="selectedItems = [...items]">Select All</button>
+      </div>
+    </div>
+
+    <div class="labels-container">
+      <div v-for="(label, index) in printLabels" :key="index" class="bin-label">
+        <svg :ref="element => setBarcodeElement(element, index)" class="bin-barcode"></svg>
+        <div class="bin-code">{{ label.itemcode }}</div>
+      </div>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, computed, onMounted, watch, nextTick } from 'vue'
+import JsBarcode from 'jsbarcode'
+import { printedpartsApi } from '@/api'
+
+const items = ref([])
+const selectedItems = ref([])
+const copies = ref(1)
+const loading = ref(true)
+const barcodeElements = ref({})
+
+onMounted(async () => {
+  try {
+    const response = await printedpartsApi.list({ perpage: 500 })
+    items.value = response.data.data || []
+    // ?item=<id> preselects one part (the Detail-page print button)
+    const preselect = new URLSearchParams(window.location.search).get('item')
+    if (preselect) {
+      const match = items.value.find(
+        candidate => String(candidate.printeditemid) === preselect)
+      if (match) selectedItems.value = [match]
+    }
+  } catch (error) {
+    console.error('Error loading parts:', error)
+  } finally {
+    loading.value = false
+  }
+})
+
+const printLabels = computed(() => {
+  const labels = []
+  for (const item of selectedItems.value) {
+    for (let copy = 0; copy < Math.max(1, copies.value); copy++) {
+      labels.push(item)
+    }
+  }
+  return labels
+})
+
+function isSelected(item) {
+  return selectedItems.value.some(
+    candidate => candidate.printeditemid === item.printeditemid)
+}
+
+function toggleItem(item) {
+  if (isSelected(item)) {
+    selectedItems.value = selectedItems.value.filter(
+      candidate => candidate.printeditemid !== item.printeditemid)
+  } else {
+    selectedItems.value = [...selectedItems.value, item]
+  }
+}
+
+function setBarcodeElement(element, index) {
+  if (element) barcodeElements.value[index] = element
+}
+
+watch(printLabels, async labels => {
+  await nextTick()
+  labels.forEach((label, index) => {
+    const element = barcodeElements.value[index]
+    if (element) {
+      // CODE128 of the short item code fits 1x0.5in with comfortable
+      // scanner tolerance; a QR at this size would be marginal.
+      JsBarcode(element, label.itemcode, {
+        format: 'CODE128',
+        displayValue: false,
+        width: 1.4,
+        height: 26,
+        margin: 0
+      })
+    }
+  })
+}, { deep: true })
+
+function print() {
+  window.print()
+}
+</script>
+
+<style scoped>
+.controls {
+  max-width: 46rem;
+  margin: 1rem auto;
+  padding: 1rem;
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-radius: 0.5rem;
+}
+.parts-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(14rem, 1fr));
+  gap: 0.5rem;
+  max-height: 20rem;
+  overflow-y: auto;
+  margin: 1rem 0;
+}
+.part-item {
+  display: flex;
+  gap: 0.5rem;
+  padding: 0.5rem;
+  border: 1px solid var(--border);
+  border-radius: 0.35rem;
+  cursor: pointer;
+}
+.part-item.selected { border-color: var(--primary); }
+.alias { color: var(--text-light); font-size: 0.85rem; }
+.selected-count { margin: 0.75rem 0; }
+.copies-label { margin-left: 1.25rem; }
+.copies-label input { width: 4rem; padding: 0.25rem; }
+.print-btn, .clear-btn, .select-all-btn {
+  margin-right: 0.5rem;
+  padding: 0.5rem 1rem;
+  cursor: pointer;
+}
+.loading-msg { color: var(--text-light); padding: 1rem; }
+
+/* screen preview of the labels */
+.labels-container { display: flex; flex-wrap: wrap; gap: 0.4rem; padding: 1rem; }
+.bin-label {
+  width: 1in;
+  height: 0.5in;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  overflow: hidden;
+  background: #fff;
+  outline: 1px dashed #bbb;
+}
+.bin-barcode { width: 0.92in; height: 0.3in; }
+.bin-code {
+  font-size: 6.5pt;
+  font-family: monospace;
+  color: #000;
+  line-height: 1;
+}
+
+/* 1in x 0.5in roll stock: one label per page */
+@media print {
+  .no-print { display: none; }
+  .labels-container { display: block; padding: 0; gap: 0; }
+  .bin-label {
+    outline: none;
+    page-break-after: always;
+    break-after: page;
+  }
+}
+</style>
+
+<style>
+@media print {
+  @page { size: 1in 0.5in; margin: 0; }
+  body { margin: 0; }
+}
+</style>