Install pi-claude-code-provider on first container start

The Pi coding agent stores installed packages under $PI_CODING_AGENT_DIR
(=/pi-agent in the image), which is a volume — so anything installed at
build time is masked at runtime. Wrap the CMD in an entrypoint that runs
`pi install npm:pi-claude-code-provider` the first time the volume is
seen and drops a marker so subsequent starts are a no-op.

Dockerfile

@@ -11,9 +11,12 @@ COPY tsconfig.json tsconfig.build.json ./
 COPY src ./src
 RUN npm run build && npm prune --omit=dev
 
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
 ENV NODE_ENV=production \
     WORKSPACE_DIR=/workspace \
     PI_CODING_AGENT_DIR=/pi-agent
 VOLUME ["/workspace", "/pi-agent"]
 
-CMD ["node", "dist/main.js"]
+CMD ["/usr/local/bin/docker-entrypoint.sh"]