chore: replace committed lib/ files with npm copy-libs script

Remove the manually committed lib/ directory and instead use npm packages.
A new `copy-libs` script copies files from node_modules/ to lib/ at build
time. Updated .gitignore, CI workflow, and README accordingly.

Author: Copilot

.github/workflows/deploy-pages.yml

@@ -26,6 +26,17 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install npm dependencies and copy libs
+        run: |
+          npm ci
+          npm run copy-libs
+
       - name: Setup Pages
         uses: actions/configure-pages@v5
 

.gitignore

@@ -2,3 +2,4 @@
 /_site/
 /Gemfile.lock
 /node_modules/
+/lib/

README.md

@@ -25,6 +25,8 @@ To test the site locally:
 2. Install dependencies:
    ```bash
    bundle install
+   npm install
+   npm run copy-libs
    ```
 
 3. Run Jekyll locally: