feat: add /healthz endpoint and test coverage for health check

Closes: #2493

internal/api/server.go

@@ -317,6 +317,10 @@ func NewServer(cfg *config.Config, authManager *auth.Manager, accessManager *sdk
 // setupRoutes configures the API routes for the server.
 // It defines the endpoints and associates them with their respective handlers.
 func (s *Server) setupRoutes() {
+	s.engine.GET("/healthz", func(c *gin.Context) {
+		c.JSON(http.StatusOK, gin.H{"status": "ok"})
+	})
+
 	s.engine.GET("/management.html", s.serveManagementControlPanel)
 	openaiHandlers := openai.NewOpenAIAPIHandler(s.handlers)
 	geminiHandlers := gemini.NewGeminiAPIHandler(s.handlers)

internal/api/server_test.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"encoding/json"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -46,6 +47,28 @@ func newTestServer(t *testing.T) *Server {
 	return NewServer(cfg, authManager, accessManager, configPath)
 }
 
+func TestHealthz(t *testing.T) {
+	server := newTestServer(t)
+
+	req := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+	rr := httptest.NewRecorder()
+	server.engine.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("unexpected status code: got %d want %d; body=%s", rr.Code, http.StatusOK, rr.Body.String())
+	}
+
+	var resp struct {
+		Status string `json:"status"`
+	}
+	if err := json.Unmarshal(rr.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to parse response JSON: %v; body=%s", err, rr.Body.String())
+	}
+	if resp.Status != "ok" {
+		t.Fatalf("unexpected response status: got %q want %q", resp.Status, "ok")
+	}
+}
+
 func TestAmpProviderModelRoutes(t *testing.T) {
 	testCases := []struct {
 		name         string