fix: remove VOLUME keyword for Railway compatibility (#2619)

Railway bans VOLUME in Dockerfiles — persistent storage is handled via
Railway volumes instead.

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

Dockerfile

@@ -83,7 +83,6 @@ ENV NODE_ENV=production \
   OPENCODE_ALLOW_ALL_MODELS=true \
   GEMINI_SANDBOX=false
 
-VOLUME ["/paperclip"]
 EXPOSE 3100
 
 ENTRYPOINT ["docker-entrypoint.sh"]