printedparts stage 12: admin settings page + settings-rail card

PrintedPartsSettings edits the four plugin settings (code prefix,
default threshold, kiosk badge policy, alert recipients) through the
core settings API; the route rides the plugin's router file and the
settings shell nests it into the rail; get_settings_cards contributes
the catalog card while the plugin is enabled.

docs/PLUGIN-LAB-PRINTEDPARTS.md

@@ -306,6 +306,20 @@ CONTRACT ADDITION, because the mailer was not on the plugin surface:
    crossing, no re-fire while below, rearm after restock (see
    `test_lowstock_alert_fires_on_crossing_only`).
 
+## Stage 12 (extension) - the admin settings page
+
+A get_settings_cards card needs a PAGE to link, which is why stage 9 deferred
+it. The page is ordinary:
+1. `frontend/src/views/settings/PrintedPartsSettings.vue` - load the four
+   keys via `settingsApi.list({category: 'printedparts'})`, save each with
+   `settingsApi.update(key, value)` (admin-gated server-side).
+2. Route in the PLUGIN's router file with path `settings/printedparts` +
+   `requiresAuth, requiresAdmin, plugin` meta - the router shell
+   automatically nests any `settings/...` path under the two-pane settings
+   rail.
+3. `get_settings_cards` on the plugin pointing at `/settings/printedparts` -
+   the card appears in the rail's catalog while the plugin is enabled.
+
 ---
 
 ## Where each pattern lives (cheat sheet)

frontend/src/router/routes/printedparts.js

@@ -31,5 +31,11 @@ export default [
     name: 'printedparts-edit',
     component: () => import('../../views/printedparts/PrintedItemForm.vue'),
     meta: { requiresAuth: true, plugin: 'printedparts' }
+  },
+  {
+    path: 'settings/printedparts',
+    name: 'settings-printedparts',
+    component: () => import('../../views/settings/PrintedPartsSettings.vue'),
+    meta: { requiresAuth: true, requiresAdmin: true, plugin: 'printedparts' }
   }
 ]

frontend/src/views/settings/PrintedPartsSettings.vue

@@ -0,0 +1,109 @@
+<template>
+  <div>
+    <div class="page-header">
+      <h2>3D Printed Parts</h2>
+    </div>
+
+    <div class="card form-card">
+      <div v-if="message" class="settings-success">{{ message }}</div>
+      <div v-if="error" class="error-message">{{ error }}</div>
+
+      <div class="form-group">
+        <label>Item code prefix</label>
+        <input v-model="values.printedparts_code_prefix" type="text"
+               class="form-control" maxlength="8" />
+        <p class="field-hint">
+          New items mint codes like {{ values.printedparts_code_prefix || '3DP' }}-0042.
+          Changing it does not rename existing items.
+        </p>
+      </div>
+
+      <div class="form-group">
+        <label>Default low-stock threshold</label>
+        <input v-model.number="values.printedparts_default_threshold"
+               type="number" min="0" class="form-control" />
+        <p class="field-hint">Seed value for new items; each item can override.</p>
+      </div>
+
+      <div class="form-group">
+        <label>Unknown badge at the kiosk</label>
+        <select v-model="values.printedparts_unknown_badge" class="form-control">
+          <option value="deny">Deny - refuse badges with no directory match</option>
+          <option value="allow">Allow - record the SSO with no name</option>
+        </select>
+      </div>
+
+      <div class="form-group">
+        <label>Low-stock alert recipients</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">
+          Comma-separated. Empty uses the site-wide alert recipients
+          (Settings &gt; System &gt; Email). Alerts fire once when an item
+          crosses its threshold; restocking above re-arms.
+        </p>
+      </div>
+
+      <button class="btn btn-primary" :disabled="saving" @click="save">
+        {{ saving ? 'Saving...' : 'Save' }}
+      </button>
+    </div>
+  </div>
+</template>
+
+<script setup>
+import { ref, onMounted } from 'vue'
+import { settingsApi } from '@/api'
+
+const KEYS = [
+  'printedparts_code_prefix',
+  'printedparts_default_threshold',
+  'printedparts_unknown_badge',
+  'printedparts_alert_email'
+]
+
+const values = ref({
+  printedparts_code_prefix: '3DP',
+  printedparts_default_threshold: 5,
+  printedparts_unknown_badge: 'deny',
+  printedparts_alert_email: ''
+})
+const saving = ref(false)
+const message = ref('')
+const error = ref('')
+
+onMounted(async () => {
+  try {
+    const response = await settingsApi.list({ category: 'printedparts' })
+    const rows = response.data.data || []
+    for (const row of rows) {
+      if (KEYS.includes(row.key)) values.value[row.key] = row.value
+    }
+    values.value.printedparts_default_threshold =
+      parseInt(values.value.printedparts_default_threshold, 10) || 0
+  } catch (loadError) {
+    error.value = 'Could not load settings'
+    console.error(loadError)
+  }
+})
+
+async function save() {
+  saving.value = true
+  message.value = ''
+  error.value = ''
+  try {
+    for (const key of KEYS) {
+      await settingsApi.update(key, String(values.value[key] ?? ''))
+    }
+    message.value = 'Settings saved'
+  } catch (saveError) {
+    error.value = saveError.response?.data?.data?.error?.message || 'Save failed'
+  } finally {
+    saving.value = false
+  }
+}
+</script>
+
+<style scoped>
+.field-hint { color: var(--text-light); font-size: 0.85rem; margin-top: 0.25rem; }
+</style>

plugins/printedparts/plugin.py

@@ -62,6 +62,19 @@ class PrintedpartsPlugin(BasePlugin):
              'printedparts'),
         ]
 
+    def get_settings_cards(self) -> List[dict]:
+        return [
+            {
+                'group': '3D Printed Parts',
+                'to': '/settings/printedparts',
+                'icon': 'box',
+                'title': '3D Parts Settings',
+                'description': 'Item code prefix, default threshold, kiosk '
+                               'badge policy, low-stock alert recipients',
+                'position': 47,
+            },
+        ]
+
     def get_reports(self) -> List[dict]:
         return [
             {