Update Docker workflows and submodule configurations

[xnetinho]

This pull request introduces significant improvements to the Docker build and deployment workflow for the project. The changes include a new GitHub Actions workflow for automated Docker publishing, updates to the frontend submodule URL, and a comprehensive refactor of the Dockerfile to optimize build stages, increase resilience, and enhance compatibility.

CI/CD Improvements:

• Added a new .github/workflows/docker-publish.yml workflow to automate building and publishing Docker images on pushes to main and tags, supporting multi-platform builds and caching for faster builds.

Submodule Management:

• Updated the frontend submodule URL in .gitmodules to point to xnetinho/NovaSDR-frontend for improved source management and reliability.

Dockerfile Refactor and Build Optimization:

• Refactored the Dockerfile with explicit multi-stage builds, including a frontend builder, Rust planner for dependency caching, backend builder, and final runtime image, improving build speed and reliability.
• Enhanced resilience for frontend builds by conditionally running npm ci or npm install based on the presence of package-lock.json.
• Unified and expanded build dependencies, added explicit driver builds for SoapySDR and RTL-SDR, and ensured runtime parity with additional libraries like libopus0.
• Corrected paths for copying binaries and resources, and streamlined environment variable setup and runtime commands in the final image.