Fix SSH tunnel Docker build for Dokploy deployment

Changes:
- Fix Dockerfile COPY path from ../secrets to secrets/ (Docker doesn't allow parent directory access)
- Create ssh-tunnel/secrets/ directory structure with comprehensive README
- Add .dockerignore for ssh-tunnel to optimize build context
- Add DOKPLOY_DEPLOYMENT.md with complete deployment guide including:
  * SSH key configuration options (repository, secrets manager, BuildKit)
  * Environment variables setup
  * Step-by-step deployment instructions
  * Troubleshooting section
  * Security best practices
- Update .gitignore to allow secrets/README.md files for documentation

This resolves the Dokploy build failure: "failed to calculate checksum of ref... /secrets/roa_oracle_server: not found"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

ssh-tunnel/Dockerfile

@@ -18,7 +18,10 @@ RUN mkdir -p /home/tunnel/.ssh && \
     chown -R tunnel:tunnel /home/tunnel
 
 # Copy SSH key and set permissions (before switching to non-root user)
-COPY ../secrets/roa_oracle_server /home/tunnel/.ssh/roa_oracle_server
+# For production deployment (Dokploy/Docker), the SSH key should be:
+# 1. Placed in ssh-tunnel/secrets/roa_oracle_server before build, OR
+# 2. Provided via BuildKit secrets (see DOKPLOY_DEPLOYMENT.md)
+COPY secrets/roa_oracle_server /home/tunnel/.ssh/roa_oracle_server
 RUN chown tunnel:tunnel /home/tunnel/.ssh/roa_oracle_server && \
     chmod 600 /home/tunnel/.ssh/roa_oracle_server