Remove configure-pages step and clarify docs

Remove the redundant 'Setup Pages' step (actions/configure-pages@v5) from the docs GitHub Actions workflow and update docs/doxygen.md to state that selecting the Pages source is a one-time repository setting. This simplifies the workflow and clarifies deployment behavior (PRs build only; pushes to main/tags deploy).

Author: ssh4net

.github/workflows/docs-pages.yml

@@ -42,9 +42,6 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
 
-      - name: Setup Pages
-        uses: actions/configure-pages@v5
-
       - name: Setup Python
         uses: actions/setup-python@v6
         with:

docs/doxygen.md

@@ -46,7 +46,7 @@ to GitHub Pages.
 Recommended setup:
 
 - In the repository settings, set **Pages** to **GitHub Actions** as the
-  source.
+  source. This is a one-time repository setting.
 - Pull requests build the docs but do not deploy.
 - Pushes to `main` and tag pushes build and deploy the site.