feat: support npm install -g in agent container (#1712)

* feat: support npm install -g in agent container (#1295)

Configure NPM_CONFIG_PREFIX to $HOME/.npm-global so that `npm install -g`
works inside the AWF agent container where /usr is mounted read-only.

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

* fix: guard NPM_CONFIG_PREFIX to preserve user-provided values

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

---------

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

Author: Mossaka

containers/agent/entrypoint.sh

@@ -681,6 +681,13 @@ AWFEOF
       echo "export GOROOT=\"${AWF_GOROOT}\"" >> "/host${SCRIPT_FILE}"
     fi
   fi
+  # Configure npm global prefix to a writable directory (since /usr is read-only)
+  # Preserve user-provided NPM_CONFIG_PREFIX if already set
+  echo 'if [ -z "${NPM_CONFIG_PREFIX:-}" ]; then' >> "/host${SCRIPT_FILE}"
+  echo '  export NPM_CONFIG_PREFIX="$HOME/.npm-global"' >> "/host${SCRIPT_FILE}"
+  echo 'fi' >> "/host${SCRIPT_FILE}"
+  echo 'mkdir -p "$NPM_CONFIG_PREFIX/bin" 2>/dev/null' >> "/host${SCRIPT_FILE}"
+  echo 'export PATH="$NPM_CONFIG_PREFIX/bin:$PATH"' >> "/host${SCRIPT_FILE}"
   # Append the actual command arguments
   # Docker CMD passes commands as ['/bin/bash', '-c', 'command_string'].
   # Instead of writing the full [bash, -c, cmd] via printf '%q' (which creates