Refactor: Migrate from Jekyll to pure HTML/CSS/JS with modern design

- Remove Jekyll build system and dependencies (_config.yml, _includes/, _sass/)
- Implement pure HTML/CSS/JS website with responsive design
- Adopt Google-style design with Google Sans Display and Roboto fonts
- Apply Google Blue accent color throughout
- Update Maven Central statistics with real download numbers
- Convert all markdown pages (.md) to static HTML pages
- Update GitHub Actions workflow to deploy static files directly
- Pages: index.html, features.html, api.html, contribute.html

This is a major refactor that simplifies the site architecture while
maintaining all existing content and improving the user experience.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: claude

.github/workflows/jekyll-gh-pages.yml

@@ -1,51 +1,35 @@
-# Sample workflow for building and deploying a Jekyll site to GitHub Pages
-name: Deploy Jekyll with GitHub Pages dependencies preinstalled
+# Deploy static site to GitHub Pages
+name: Deploy to GitHub Pages
 
 on:
-  # Runs on pushes targeting the default branch
   push:
     branches: ["main"]
-
-  # Allows you to run this workflow manually from the Actions tab
   workflow_dispatch:
 
-# Sets permissions of the GITHUB_TOKEN to allow deployment to GitHub Pages
 permissions:
   contents: read
   pages: write
   id-token: write
 
-# Allow only one concurrent deployment, skipping runs queued between the run in-progress and latest queued.
-# However, do NOT cancel in-progress runs as we want to allow these production deployments to complete.
 concurrency:
   group: "pages"
   cancel-in-progress: false
 
 jobs:
-  # Build job
-  build:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v3
-      - name: Setup Pages
-        uses: actions/configure-pages@v3
-      - name: Build with Jekyll
-        uses: actions/jekyll-build-pages@v1
-        with:
-          source: ./
-          destination: ./_site
-      - name: Upload artifact
-        uses: actions/upload-pages-artifact@v1
-
-  # Deployment job
   deploy:
     environment:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     runs-on: ubuntu-latest
-    needs: build
     steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: '.'
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4