printedparts stage 3: read API + list page (first visible win)

GET /items (paginated, search across code/name/description/bin,
lowstock filter) and GET /items/<id> with recent transactions, both
open reads. printedpartsApi client, router file repointed at the
renamed views, PrintedItemsList with image thumbs and a red/green
quantity badge against the per-item threshold. Nav entry '3D Parts'
with a new 'box' Lucide icon mapping (the sidebar renders nothing for
unknown icon names - lab gotcha).

frontend/src/api/index.js

@@ -1126,3 +1126,13 @@ export const measuringtoolsApi = {
     }
   }
 }
+
+// 3D printed parts (printedparts plugin)
+export const printedpartsApi = {
+  list(params = {}) {
+    return api.get('/printedparts/items', { params })
+  },
+  get(printeditemid) {
+    return api.get(`/printedparts/items/${printeditemid}`)
+  }
+}