Align docs workflow with AgentPin pattern

- configure-pages step first (enables Pages programmatically)
- Single-job deploy instead of split build/deploy
- zensical build --clean for reproducible output
- actions/upload-pages-artifact@v4 and actions/checkout@v5 to match the
  versions AgentPin runs in production
- Floating python-version: 3.x

Kept relative to AgentPin's workflow:
- workflow_dispatch for manual rebuilds
- concurrency group: pages (cancel-in-progress: false) so a doc bump
  during deploy queues instead of cancelling
- cp docs/CNAME -> site/CNAME instead of echo (docs/CNAME stays the
  single source of truth in the repo)

Author: jaschadub

.github/workflows/docs.yml

@@ -1,8 +1,9 @@
-name: Docs
+name: Documentation
 
 on:
   push:
-    branches: [main]
+    branches:
+      - main
     paths:
       - "docs/**"
       - "zensical.toml"
@@ -19,33 +20,22 @@ concurrency:
   cancel-in-progress: false
 
 jobs:
-  build:
-    name: Build Zensical site
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/configure-pages@v5
+      - uses: actions/checkout@v5
       - uses: actions/setup-python@v5
         with:
-          python-version: "3.12"
-      - name: Install Zensical
-        run: |
-          python -m pip install --upgrade pip
-          pip install zensical
-      - name: Build
-        run: zensical build
-      - name: Copy CNAME to site root
-        run: cp docs/CNAME site/CNAME
-      - uses: actions/upload-pages-artifact@v3
+          python-version: 3.x
+      - run: pip install zensical
+      - run: zensical build --clean
+      - run: cp docs/CNAME site/CNAME
+      - uses: actions/upload-pages-artifact@v4
         with:
           path: site
-
-  deploy:
-    name: Deploy to GitHub Pages
-    needs: build
-    runs-on: ubuntu-latest
-    environment:
-      name: github-pages
-      url: ${{ steps.deployment.outputs.page_url }}
-    steps:
-      - id: deployment
-        uses: actions/deploy-pages@v4
+      - uses: actions/deploy-pages@v4
+        id: deployment