fix: Only run npm when building from source (#758)

scripts/npm.py

@@ -1,9 +1,15 @@
 import subprocess
+from pathlib import Path
 
 from hatchling.builders.hooks.plugin.interface import BuildHookInterface
 
 
 class NpmBuildHook(BuildHookInterface):
     def initialize(self, version, build_data):
-        subprocess.check_output("npm ci", shell=True)
-        subprocess.check_output("npm run build", shell=True)
+        is_source = Path(self.root, ".git").exists()
+        app_js_exists = Path(
+            self.root, "src", "pytest_html", "resources", "app.js"
+        ).exists()
+        if is_source or not app_js_exists:
+            subprocess.run("npm ci", capture_output=True, check=True, shell=True)
+            subprocess.run("npm run build", capture_output=True, check=True, shell=True)