feat: add engine identifier to /api/stats and /api/health

Both backends now return an 'engine' field ('node' or 'go') in
/api/stats and /api/health responses so the frontend can display
which backend is running.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cmd/server/routes.go

@@ -264,6 +264,7 @@ func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
 
 	writeJSON(w, map[string]interface{}{
 		"status":      "ok",
+		"engine":      "go",
 		"uptime":      int(uptime),
 		"uptimeHuman": fmt.Sprintf("%dh %dm", int(uptime)/3600, (int(uptime)%3600)/60),
 		"memory": map[string]interface{}{
@@ -314,6 +315,7 @@ func (s *Server) handleStats(w http.ResponseWriter, r *http.Request) {
 		"totalNodesAllTime":  stats.TotalNodesAllTime,
 		"totalObservers":     stats.TotalObservers,
 		"packetsLastHour":    stats.PacketsLastHour,
+		"engine":             "go",
 		"counts":             counts,
 	}
 	writeJSON(w, result)

cmd/server/routes_test.go

@@ -35,6 +35,9 @@ func TestHealthEndpoint(t *testing.T) {
 	if body["status"] != "ok" {
 		t.Errorf("expected status ok, got %v", body["status"])
 	}
+	if body["engine"] != "go" {
+		t.Errorf("expected engine go, got %v", body["engine"])
+	}
 }
 
 func TestStatsEndpoint(t *testing.T) {
@@ -54,6 +57,9 @@ func TestStatsEndpoint(t *testing.T) {
 	if body["totalNodes"] != float64(3) {
 		t.Errorf("expected 3 nodes, got %v", body["totalNodes"])
 	}
+	if body["engine"] != "go" {
+		t.Errorf("expected engine go, got %v", body["engine"])
+	}
 }
 
 func TestPacketsEndpoint(t *testing.T) {

server.js

@@ -471,6 +471,7 @@ app.get('/api/health', (req, res) => {
 
   res.json({
     status: 'ok',
+    engine: 'node',
     uptime: Math.round(uptime),
     uptimeHuman: `${Math.floor(uptime / 3600)}h ${Math.floor((uptime % 3600) / 60)}m`,
     memory: {
@@ -885,7 +886,7 @@ app.get('/api/stats', (req, res) => {
     const r = db.db.prepare(`SELECT COUNT(*) as count FROM nodes WHERE role = ? AND last_seen > ?`).get(role, sevenDaysAgo);
     counts[role + 's'] = r.count;
   }
-  res.json({ ...stats, counts });
+  res.json({ ...stats, engine: 'node', counts });
 });
 
 app.get('/api/packets', (req, res) => {

test-server-routes.js

@@ -171,12 +171,14 @@ seedTestData();
   await t('GET /api/health', async () => {
     const r = await request(app).get('/api/health').expect(200);
     assert(r.body.status, 'should have status');
+    assert(r.body.engine === 'node', 'health should include engine=node');
   });
 
   // --- Stats ---
   await t('GET /api/stats', async () => {
     const r = await request(app).get('/api/stats').expect(200);
     assert(typeof r.body === 'object', 'should return stats');
+    assert(r.body.engine === 'node', 'stats should include engine=node');
   });
 
   // --- Perf ---