Add device inventory refresh endpoint and auto-refresh UI

test/server/device-inventory.test.js

@@ -30,14 +30,21 @@ test('device inventory discovers, merges, persists metadata and expires anonymou
     ], current.toISOString()),
     error: null,
   };
+  let observeCalls = 0;
   const service = createDeviceInventoryService({
     store,
-    observe: async () => observation,
+    observe: async () => {
+      observeCalls += 1;
+      return observation;
+    },
     vendor,
     now: () => current,
   });
 
-  let snapshot = await service.refresh();
+  const [firstRefresh, sharedRefresh] = await Promise.all([service.refresh(), service.refresh()]);
+  let snapshot = firstRefresh;
+  assert.strictEqual(sharedRefresh, firstRefresh);
+  assert.equal(observeCalls, 1);
   assert.equal(snapshot.devices.length, 1);
   assert.equal(snapshot.devices[0].manufacturer, 'Example Devices');
   assert.equal(snapshot.devices[0].status, 'online');