printedparts stage 13: pick alert recipients from shopdb users

Contract 0.13.0 puts the User model on the plugin surface. The
settings page gains a checkbox picker over the user list; selected
users receive low-stock alerts at their account email, merged and
deduped with the free-text address list, inactive accounts skipped,
site alert_recipients still the fallback when both are empty.

frontend/src/views/settings/PrintedPartsSettings.vue

@@ -34,7 +34,23 @@
       </div>
 
       <div class="form-group">
-        <label>Low-stock alert recipients</label>
+        <label>Alert shopdb users</label>
+        <div class="user-picker">
+          <label v-for="candidate in users" :key="candidate.userid" class="user-row">
+            <input type="checkbox" :value="String(candidate.userid)"
+                   v-model="selectedUserids" />
+            <span>{{ candidate.username }}</span>
+            <span class="user-email">{{ candidate.email }}</span>
+          </label>
+          <p v-if="users.length === 0" class="field-hint">No users loaded</p>
+        </div>
+        <p class="field-hint">
+          Selected users receive low-stock alerts at their account email.
+        </p>
+      </div>
+
+      <div class="form-group">
+        <label>Additional alert emails</label>
         <input v-model="values.printedparts_alert_email" type="text"
                class="form-control" placeholder="parts-team@example.com, lead@example.com" />
         <p class="field-hint">
@@ -53,21 +69,25 @@
 
 <script setup>
 import { ref, onMounted } from 'vue'
-import { settingsApi } from '@/api'
+import { settingsApi, usersApi } from '@/api'
 
 const KEYS = [
   'printedparts_code_prefix',
   'printedparts_default_threshold',
   'printedparts_unknown_badge',
-  'printedparts_alert_email'
+  'printedparts_alert_email',
+  'printedparts_alert_userids'
 ]
 
 const values = ref({
   printedparts_code_prefix: '3DP',
   printedparts_default_threshold: 5,
   printedparts_unknown_badge: 'deny',
-  printedparts_alert_email: ''
+  printedparts_alert_email: '',
+  printedparts_alert_userids: ''
 })
+const users = ref([])
+const selectedUserids = ref([])
 const saving = ref(false)
 const message = ref('')
 const error = ref('')
@@ -81,6 +101,11 @@ onMounted(async () => {
     }
     values.value.printedparts_default_threshold =
       parseInt(values.value.printedparts_default_threshold, 10) || 0
+    selectedUserids.value = (values.value.printedparts_alert_userids || '')
+      .split(',').map(id => id.trim()).filter(Boolean)
+    const usersResponse = await usersApi.list()
+    users.value = (usersResponse.data.data || []).filter(
+      candidate => candidate.isactive && candidate.email)
   } catch (loadError) {
     error.value = 'Could not load settings'
     console.error(loadError)
@@ -92,6 +117,7 @@ async function save() {
   message.value = ''
   error.value = ''
   try {
+    values.value.printedparts_alert_userids = selectedUserids.value.join(',')
     for (const key of KEYS) {
       await settingsApi.update(key, String(values.value[key] ?? ''))
     }
@@ -106,4 +132,21 @@ async function save() {
 
 <style scoped>
 .field-hint { color: var(--text-light); font-size: 0.85rem; margin-top: 0.25rem; }
+.user-picker {
+  max-height: 12rem;
+  overflow-y: auto;
+  border: 1px solid var(--border);
+  border-radius: 0.35rem;
+  padding: 0.5rem;
+  display: flex;
+  flex-direction: column;
+  gap: 0.35rem;
+}
+.user-row {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  cursor: pointer;
+}
+.user-email { color: var(--text-light); font-size: 0.85rem; }
 </style>