feat: documentation site

Docusaurus 3 docs-only site at docsite/, served statically by nginx under
/docs on the marketing host. Covers getting started (self-hosted install
through first server and first licence), the control plane, Vantage HQ,
a reference section and operations.

Wired into docker-compose.site.yml as docsite (3005:80) and into the
image build workflow, rebuilding on its own directory only. Never added
to the self-hosted compose file.

.gitea/workflows/server-deploy.yml

@@ -81,11 +81,13 @@ jobs:
                   flag sitesvc   '^(sitesvc/|shared/|go\.work)'
                   flag admin     '^(admin/|shared/|go\.work)'
 
-                  # The three Next images use their own directory as the build
-                  # context, so nothing outside it can affect them.
+                  # The three Next images and the docs site use their own
+                  # directory as the build context, so nothing outside it can
+                  # affect them.
                   flag web       '^web/'
                   flag site      '^site/'
                   flag adminsite '^adminsite/'
+                  flag docsite   '^docsite/'
 
             - name: Log in to registry
               run: |
@@ -152,3 +154,18 @@ jobs:
                     -t "$IMAGE" \
                     -f adminsite/Dockerfile adminsite/
                   docker push "$IMAGE"
+
+            - name: Build and push docsite image
+              if: steps.changed.outputs.docsite == 'true'
+              run: |
+                  IMAGE="${{ vars.DOCKER_HOST }}/${{ github.repository_owner }}/vantage/docsite:latest"
+                  # DOCS_BASE_URL must match the proxy location that routes to
+                  # this container and the directory the image serves from.
+                  docker build \
+                    --build-arg DOCS_URL="${{ vars.DOCS_URL }}" \
+                    --build-arg DOCS_BASE_URL="${{ vars.DOCS_BASE_URL }}" \
+                    --build-arg APP_URL="${{ vars.APP_URL }}" \
+                    --build-arg HQ_URL="${{ vars.HQ_URL }}" \
+                    -t "$IMAGE" \
+                    -f docsite/Dockerfile docsite/
+                  docker push "$IMAGE"