Add GitHub Actions Workflow for Fabrication, Renders, and GitHub Pages

[slintak]

This pull request adds a fully working GitHub Actions CI workflow for the LinHT-HW project.

The new workflow automates the following steps on each push to main:

• Generates fabrication files (Gerbers, BOM, pick-and-place)
• Renders schematic and PCB 3D previews
• Creates STEP and VRML 3D model
• Renders a simple presentation web page using Jinja2
• Publishes results to GitHub Pages

This allows for automatic documentation and file generation whenever changes are pushed to the repository.

You can view the first successful run here: https://github.com/M17-Project/LinHT-hw/actions/runs/16645149458

Note: This preview job failed only because GitHub Pages cannot be published from a branch other than main. This will resolve automatically after merging.