chore: migrate package manager from npm to pnpm

GEMINI.md

@@ -18,7 +18,7 @@ This project uses [Vitest](https://vitest.dev/) for testing. The tests are locat
 To run the tests locally, use the following command:
 
 ```bash
-npm test
+pnpm test
 ```
 
 ### Testing Pipeline
@@ -28,6 +28,6 @@ The tests are automatically run on every push and workflow dispatch using a Gite
 The Gitea workflow does the following:
 
 1.  Checks out the code.
-2.  Sets up Node.js.
-3.  Installs the dependencies using `npm install`.
-4.  Runs the tests using `npm test`.
+2.  Sets up Node.js and pnpm.
+3.  Installs the dependencies using `pnpm install`.
+4.  Runs the tests using `pnpm test`.