Fix SDK embed ENOENT when package.json missing (closes #5226)

- Wrap package.json read in try/catch to handle missing file gracefully
- Use defaults (APP_NAME=pi, CONFIG_DIR_NAME=.pi, etc.) when package.json not found
- Preserves rebranding via piConfig when package.json exists
- Only ignores ENOENT; other errors still throw

packages/coding-agent/src/config.ts

@@ -452,7 +452,13 @@ interface PackageJson {
 	};
 }
 
-const pkg = JSON.parse(readFileSync(getPackageJsonPath(), "utf-8")) as PackageJson;
+let pkg: PackageJson = {};
+try {
+	pkg = JSON.parse(readFileSync(getPackageJsonPath(), "utf-8")) as PackageJson;
+} catch (e: unknown) {
+	const err = e as NodeJS.ErrnoException;
+	if (err.code !== "ENOENT") throw e;
+}
 
 const piConfigName: string | undefined = pkg.piConfig?.name;
 export const PACKAGE_NAME: string = pkg.name || "@earendil-works/pi-coding-agent";