fix(coding-agent): use ESM resolution for extension alias fallback (#1821)

The previous fix (83b57924) replaced require.resolve() with bare
specifier fallbacks to avoid ERR_PACKAGE_PATH_NOT_EXPORTED for ESM-only
packages like pi-ai. However, bare specifiers are not valid jiti alias
targets, breaking extension loading in global npm installs.

Use import.meta.resolve() as the fallback instead. It respects the
"import" exports condition and returns a real file path.

packages/coding-agent/package.json

@@ -94,6 +94,6 @@
 		"directory": "packages/coding-agent"
 	},
 	"engines": {
-		"node": ">=20.0.0"
+		"node": ">=20.6.0"
 	}
 }