Add JSON validation middleware to ensure valid API responses

- Created JSONValidationMiddleware that validates all JSON responses
- Ensures that even on timeout or internal errors, a valid JSON error response is returned
- Applied to all API endpoints including /status.json
- Prevents client-side JSON parse errors when server encounters issues

internal/server/routes.go

@@ -23,7 +23,7 @@ func (s *Server) setupRoutes() {
 	// Routes
 	r.Get("/", s.handleRoot())
 	r.Get("/status", s.handleStatusHTML())
-	r.Get("/status.json", s.handleStatusJSON())
+	r.Get("/status.json", JSONValidationMiddleware(s.handleStatusJSON()).ServeHTTP)
 
 	// AS and prefix detail pages
 	r.Get("/as/{asn}", s.handleASDetail())
@@ -33,6 +33,7 @@ func (s *Server) setupRoutes() {
 
 	// API routes
 	r.Route("/api/v1", func(r chi.Router) {
+		r.Use(JSONValidationMiddleware)
 		r.Get("/stats", s.handleStats())
 		r.Get("/ip/{ip}", s.handleIPLookup())
 		r.Get("/as/{asn}", s.handleASDetailJSON())