ci: auto-publish Doxygen HTML to Codeberg Pages on main

New .gitea/workflows/doxygen-pages.yml runs on every push to main that
touches the public headers, Doxyfile, the markdown-link filter, any
doc/**/*.md, README.md, or the workflow itself.  It reuses the existing
ci-cpp container image and the existing CODEBERG_TOKEN secret already
used by mirror-to-codeberg.yml — no new secret setup needed.

The job force-pushes an orphan commit to the `pages` branch on
codeberg.org/TMoussa/ConformalLabpp, which Codeberg Pages serves from
https://tmoussa.codeberg.page/ConformalLabpp/ (verified live).

README.md gains a Doxygen badge and a Documentation table row pointing
at the Pages URL.  locked-vs-flexible.md (the reviewer-facing doc) is
updated to mention the Pages URL next to the Doxygen-coverage gap.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/doxygen-pages.yml

@@ -0,0 +1,78 @@
+name: Doxygen → Codeberg Pages
+
+# Auto-publish Doxygen HTML to https://tmoussa.codeberg.page/ConformalLabpp/
+# every time the public API or docs source changes on main.
+#
+# Pattern: mirrors mirror-to-codeberg.yml — reuses the existing
+# CODEBERG_TOKEN secret + HTTPS push.  No new secret setup required.
+#
+# Trigger: push to main that touches code/include/**, Doxyfile, the
+# filter script, doc/**/*.md, README.md, or this workflow file.  Also
+# manually triggerable via workflow_dispatch.
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - "code/include/**"
+      - "Doxyfile"
+      - "scripts/doxygen-md-filter.sh"
+      - "doc/**/*.md"
+      - "README.md"
+      - "CLAUDE.md"
+      - ".gitea/workflows/doxygen-pages.yml"
+  workflow_dispatch: {}
+
+jobs:
+  publish:
+    runs-on: eulernest
+    container:
+      image: git.eulernest.eu/conformallab/ci-cpp:latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure CMake (Doxygen target only — no compiler needed)
+        run: cmake -S code -B build
+
+      - name: Build Doxygen HTML
+        run: |
+          cmake --build build --target doc
+          test -f doc/doxygen/html/index.html
+          warnings=$(wc -l < doc/doxygen/doxygen-warnings.log)
+          echo "DOC ▸ Doxygen warnings: $warnings"
+          if [ "$warnings" -gt 0 ]; then
+            echo "::warning::Doxygen produced $warnings warning(s) — review doc/doxygen/doxygen-warnings.log"
+            head -30 doc/doxygen/doxygen-warnings.log
+          fi
+
+      - name: Publish HTML to codeberg pages branch
+        env:
+          CODEBERG_TOKEN: ${{ secrets.CODEBERG_TOKEN }}
+        run: |
+          set -eu
+          # Build the publish payload in a clean scratch dir so the
+          # orphan branch contains only the Doxygen output (and a
+          # marker README), never any build/source artefacts.
+          publish_dir=$(mktemp -d)
+          cp -r doc/doxygen/html/. "$publish_dir/"
+
+          cat > "$publish_dir/README.txt" <<EOF
+          conformallab++ — Doxygen HTML API documentation.
+          Auto-generated by .gitea/workflows/doxygen-pages.yml from
+          commit ${GITHUB_SHA:-$(git rev-parse HEAD)} on $(date -Iseconds).
+          Source: https://codeberg.org/TMoussa/ConformalLabpp
+          EOF
+
+          cd "$publish_dir"
+          git init -q -b pages
+          git config user.email "ci@eulernest"
+          git config user.name  "conformallab CI"
+          git add -A
+          git commit -q -m "Auto-publish: Doxygen HTML for ${GITHUB_SHA:-HEAD}"
+          # Force-push: the pages branch is a publish target, history
+          # is not interesting (we only ever serve the latest snapshot).
+          git push -f \
+            "https://TMoussa:${CODEBERG_TOKEN}@codeberg.org/TMoussa/ConformalLabpp.git" \
+            pages:pages