fix: fix Antora Docker image and playbook for local builds

- Install npm packages to /opt/antora (not /antora which gets
  volume-mounted over)
- Set NODE_PATH=/opt/antora/node_modules so Antora finds extensions
- Use /opt/antora/node_modules/.bin/antora as entrypoint (not npx)
- Fix playbook content source url to /antora (git repo root)

Verified locally: 19 HTML pages, 12 Mermaid SVG diagrams rendered
via Chromium inside the container.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: michalharakal

docs/.docker/Dockerfile

@@ -10,26 +10,28 @@ RUN apk add --no-cache chromium font-noto
 ENV PUPPETEER_EXECUTABLE_PATH=/usr/bin/chromium-browser \
     PUPPETEER_SKIP_DOWNLOAD=true
 
-WORKDIR /antora
-
-# Install Antora + extensions + mermaid-cli in one layer
-RUN npm i --save-exact \
+# Install Antora + extensions to /opt/antora (not /antora which gets volume-mounted)
+WORKDIR /opt/antora
+RUN npm init -y && npm i --save-exact \
       @antora/cli@3.1 \
       @antora/site-generator@3.1 \
       asciidoctor-kroki@0.18 \
       @mermaid-js/mermaid-cli@11 \
     && npm cache clean --force
 
-# Mermaid-cli config: use installed Chromium, no sandbox (container)
+# Make installed modules visible when workdir is the mounted project
+ENV NODE_PATH=/opt/antora/node_modules
+
+# Mermaid-cli config
 RUN echo '{ \
   "executablePath": "/usr/bin/chromium-browser", \
   "args": ["--no-sandbox", "--disable-gpu", "--disable-dev-shm-usage"] \
-}' > /antora/puppeteer-config.json
+}' > /opt/antora/puppeteer-config.json
 
-# Pre-generate a simple diagram to warm up and verify the stack works
+# Verify mermaid works
 RUN echo 'graph TD; A-->B;' > /tmp/test.mmd \
-    && npx mmdc -i /tmp/test.mmd -o /tmp/test.svg -p /antora/puppeteer-config.json \
+    && npx mmdc -i /tmp/test.mmd -o /tmp/test.svg -p /opt/antora/puppeteer-config.json \
     && rm /tmp/test.mmd /tmp/test.svg
 
-ENTRYPOINT ["npx", "antora"]
+ENTRYPOINT ["/opt/antora/node_modules/.bin/antora"]
 CMD ["--stacktrace", "antora-playbook.yml"]

docs/antora-playbook.yml

@@ -4,7 +4,7 @@ site:
 
 content:
   sources:
-    - url: .
+    - url: /antora
       start_path: docs
       branches: HEAD