chore: migrate package manager from npm to pnpm (#110)

This PR migrates the package manager from `npm` to `pnpm`.

### Changes:
- Replaced `package-lock.json` with `pnpm-lock.yaml` and `pnpm-workspace.yaml`.
- Updated `.gitea/workflows/test.yaml` to include `pnpm/action-setup@v4` and use `pnpm install` / `pnpm test`.
- Updated `renovate.json` to match `pnpm` manager and execute `pnpm install --frozen-lockfile` and `pnpm run build`.
- Updated `.pre-commit-config.yaml` to exclude `pnpm-lock.yaml` from `pretty-format-yaml`.
- Updated documentation in `README.md` and `GEMINI.md`.
- Rebuilt `dist/index.js`.Reviewed-on: #110

README.md

@@ -84,7 +84,7 @@ This project includes a build step to prepare the action for use.
 ### Why a Build Step?
 
 We use a build step to compile the JavaScript code and its dependencies into a single, self-contained file (`dist/index.js`). This approach is chosen for the following reasons:
-1.  **Zero-configuration at Runtime:** By bundling everything, the action runner doesn't need to run `npm install`, which speeds up the action execution.
+1.  **Zero-configuration at Runtime:** By bundling everything, the action runner doesn't need to run `pnpm install` or `npm install`, which speeds up the action execution.
 2.  **Reliability:** It guarantees that the exact versions of dependencies tested during development are used in the action, avoiding potential issues with version updates or missing packages.
 3.  **Standard Practice:** This is a recommended practice for JavaScript-based GitHub/Gitea Actions.
 
@@ -100,8 +100,8 @@ We chose [`@vercel/ncc`](https://github.com/vercel/ncc) as the compiler because:
 If you modify `index.js` or change dependencies, you must rebuild the project before committing:
 
 ```bash
-npm install
-npm run build
+pnpm install
+pnpm run build
 ```
 
 This will update the `dist/index.js` file, which should be committed to the repository.