Add DocFX documentation site with GitHub Pages deployment

Replace bloated README with concise quick-start and link to full docs.
Move all detailed examples and guides into docs/articles/:

- Getting Started (setup, config, DI, basic auth)
- HTML & URL to PDF (Chromium features, cookies, page properties)
- Screenshots (HTML/URL capture, format/quality options)
- Office Conversion (LibreOffice options, image compression, watermarks)
- PDF Manipulation (standalone operations, cross-cutting options)
- Advanced Features (webhooks, value objects, multi-URL merge)

DocFX auto-generates API reference from XML doc comments.
GitHub Actions workflow deploys to GitHub Pages on push to
master/develop when docs or source changes.

Author: Jaben

.github/workflows/docs.yml

@@ -0,0 +1,56 @@
+name: Build and Deploy Docs
+
+on:
+  push:
+    branches: [master, develop]
+    paths:
+      - 'docs/**'
+      - 'src/**/*.cs'
+      - 'src/**/*.csproj'
+      - '.github/workflows/docs.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v4
+      with:
+        dotnet-version: 8.x
+
+    - name: Install DocFX
+      run: dotnet tool install -g docfx
+
+    - name: Build docs
+      run: docfx docs/docfx.json
+
+    - name: Upload artifact
+      uses: actions/upload-pages-artifact@v3
+      with:
+        path: docs/_site
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+    - name: Deploy to GitHub Pages
+      id: deployment
+      uses: actions/deploy-pages@v4