fix: uninstall yarn 1.x before corepack prepare and fix corepack indent

npm_install.py

@@ -2173,6 +2173,9 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
             # METHOD 1: Corepack (recommended for Yarn 4.x)
             if shutil.which("corepack"):
                 try:
+                    # Uninstall old yarn 1.x to prevent conflicts
+                    subprocess.run(["npm", "uninstall", "-g", "yarn"], check=False, cwd="/tmp")
+                    
                     # Enable corepack
                     subprocess.run(
                         ["corepack", "enable"],
@@ -2201,13 +2204,13 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
                         
                         # Check version
                         if shutil.which("yarn"):
-                                major = _get_yarn_major_version(["yarn"])
-                                
-                        if major and major >= 4:
-                            if DEBUG:
-                                print(f"   ✓ Yarn {major}.x installed via corepack")
-                            os.chdir(original_cwd)
-                            return True
+                            major = _get_yarn_major_version(["yarn"])
+                            
+                            if major and major >= 4:
+                                if DEBUG:
+                                    print(f"   ✓ Yarn {major}.x installed via corepack")
+                                os.chdir(original_cwd)
+                                return True
                 except Exception as e:
                     if DEBUG:
                         print(f"   ⚠ Corepack method failed: {e}")