fix: run opencode-ai postinstall script after npm install

The node base image has npm configured with ignore-scripts or the new
opencode-ai versions require explicit postinstall execution. Running
the postinstall manually after npm install ensures opencode --version
works regardless of npm configuration.

Dockerfile

@@ -13,6 +13,7 @@ RUN apt-get update && \
     useradd -m -u 1000 -g 1000 -s /usr/bin/bash opencode; \
     npm update -g --no-fund --no-audit && \
     npm install -g --no-fund --no-audit opencode-ai@1.17.13 n2-soul@9.0.9 && \
+    cd /usr/local/lib/node_modules/opencode-ai && node postinstall.mjs && \
     npm cache clean --force && \
     chown -R 1000:1000 /usr/local/lib/node_modules/n2-soul/