Refactor CI/CD Workflow: Add Docker Multi-Arch Build & Modernize Build/Test Steps

[mryash-dev]

This PR refactors the existing GitHub Actions workflow to improve CI/CD automation and add Docker multi-architecture image builds. Key changes include:

✅ Improvements:

• Modular Jobs: Split into build-js, build-js-windows, test, and build-docker jobs for better clarity and separation of concerns.
• Multi-Python Matrix: Runs Django tests on Python versions 3.8 – 3.11 using matrix strategy.
• Docker Metadata: Uses docker/metadata-action for consistent and semantically versioned image tags.
• Artifact Handling: Uses GitHub Actions artifact upload/download to share built JavaScript assets between jobs.
• Modern Actions: Migrated to latest action versions (checkout@v4, setup-node@v4, setup-python@v5, etc.)
• Linting + Testing: ESLint, unit tests, flake8, and Django test suite are integrated.
• Docker Build & Push: Adds Docker buildx support (multi-arch ready), and pushes images to Docker Hub.

@yasithdev @lahirujayathilake @smarru I'd love to hear any ideas you guys have!