ENH: Add JupyterLite CI/CD infrastructure

[natinew77-creator]

Tracking Issue: #13929

What does this implement/fix?

• Introduces the foundational GitHub Actions workflow (jupyterlite.yml) to automatically build a JupyterLite deployment.
• Verifies that we can successfully build a Wasm-based JupyterLab environment containing the MNE-Python examples/ directory.
• This represents the first milestone (Week 4) of my GSoC timeline to enable interactive "Try in Browser" documentation.

Additional information

• Currently, this workflow builds with the default pyodide kernel. In the upcoming weeks, I will switch this out for the xeus-python kernel to better handle MNE-Python's dependencies.
• I tested the build artifact locally via python -m http.server, and the WebAssembly environment successfully boots up.