fix: resolve MCP server startup crash on macOS (issue #46)

- Skip 0-byte cached binaries in cli.js by adding fs.statSync size check
  to prevent spawn ENOEXEC when a corrupted/incomplete download is cached
- Fix Dart fallback import in dart/bin/server.dart to use the correct
  local package name flutter_skill_npm (matches dart/pubspec.yaml)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mlab817

packaging/npm/bin/cli.js

@@ -84,7 +84,7 @@ async function main() {
   const localBinaryPath = getLocalBinaryPath();
 
   // Try to use existing native binary
-  if (localBinaryPath && fs.existsSync(localBinaryPath)) {
+  if (localBinaryPath && fs.existsSync(localBinaryPath) && fs.statSync(localBinaryPath).size > 0) {
     // Always ensure the execute bit is set before spawning.
     // postinstall chmodSync can silently fail on some npm configurations
     // (e.g. restricted sandbox, npm run as root on certain macOS setups),

packaging/npm/dart/bin/server.dart

@@ -1,3 +1,3 @@
-import 'package:flutter_skill/src/cli/server.dart';
+import 'package:flutter_skill_npm/src/cli/server.dart';
 
 void main(List<String> args) => runServer(args);