Fix Chart.js loading and add favicon support

- Switch from chart.min.js to chart.umd.js for proper module loading
- Add favicon.ico file and proper serving
- Add favicon link in HTML head to prevent 404 errors

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/server/server.go

@@ -81,8 +81,15 @@ func (s *Server) serveIndex(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) serveFavicon(w http.ResponseWriter, r *http.Request) {
+	data, err := s.staticFiles.ReadFile("static/favicon.ico")
+	if err != nil {
+		w.Header().Set("Content-Type", "image/x-icon")
+		w.WriteHeader(http.StatusNotFound)
+		return
+	}
+
 	w.Header().Set("Content-Type", "image/x-icon")
-	w.WriteHeader(http.StatusNotFound)
+	w.Write(data)
 }
 
 func (s *Server) getAircraft(w http.ResponseWriter, r *http.Request) {