✨ feat(server): add /api/healthz endpoint with rich health info (#20)

Adds Kubernetes-style /api/healthz endpoint with status/version/uptime_seconds/timestamp.

Non-breaking — /api/health preserved. Includes unit test (passes locally) and BDD scenario (validated by CI).

Généré ~95% en autonomie par Mistral Vibe via workspace ICM ~/Work/Vibe/workspaces/healthz-feature/.

Co-authored-by: Gabriel Radureau <arcodange@gmail.com>
Co-committed-by: Gabriel Radureau <arcodange@gmail.com>

pkg/server/server.go

@@ -64,6 +64,7 @@ type Server struct {
 	validator      *validation.Validator
 	userRepo       user.UserRepository
 	userService    user.UserService
+	startedAt      time.Time
 }
 
 func NewServer(cfg *config.Config, readyCtx context.Context) *Server {
@@ -89,6 +90,7 @@ func NewServer(cfg *config.Config, readyCtx context.Context) *Server {
 		validator:   validator,
 		userRepo:    userRepo,
 		userService: userService,
+		startedAt:   time.Now(),
 	}
 	s.setupRoutes()
 	return s
@@ -137,6 +139,9 @@ func (s *Server) setupRoutes() {
 	// Version endpoint at root level
 	s.router.Get("/api/version", s.handleVersion)
 
+	// Kubernetes-style health endpoint at root level
+	s.router.Get("/api/healthz", s.handleHealthz)
+
 	// API routes
 	s.router.Route("/api/v1", func(r chi.Router) {
 		r.Use(s.getAllMiddlewares()...)
@@ -358,6 +363,34 @@ func (s *Server) handleVersion(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// HealthzResponse represents the Kubernetes-style health check response
+type HealthzResponse struct {
+	Status        string    `json:"status"`
+	Version       string    `json:"version"`
+	UptimeSeconds int64     `json:"uptime_seconds"`
+	Timestamp     time.Time `json:"timestamp"`
+}
+
+// handleHealthz godoc
+//
+//	@Summary		Kubernetes-style health check
+//	@Description	Returns rich health info for liveness/readiness probes
+//	@Tags			System/Health
+//	@Produce		json
+//	@Success		200	{object}	HealthzResponse
+//	@Router			/healthz [get]
+func (s *Server) handleHealthz(w http.ResponseWriter, r *http.Request) {
+	log.Trace().Msg("Healthz check requested")
+	resp := HealthzResponse{
+		Status:        "healthy",
+		Version:       version.Version,
+		UptimeSeconds: int64(time.Since(s.startedAt).Seconds()),
+		Timestamp:     time.Now().UTC(),
+	}
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(resp)
+}
+
 func (s *Server) Router() http.Handler {
 	return s.router
 }