Add STEM Lecture Notes Typst template

[NitraxMathematicalKeyboard]

Summary

Adds the open-source stem-lecture-notes Typst template to the community index.

Template

• Source: https://github.com/NitraxMathematicalKeyboard/stem-lecture-notes-myst
• Engine: Typst
• License: MIT
• Intended use: STEM lecture notes, course handouts, scientific memos, and exam review sheets
• Formats tested: A4 and US Letter

Validation

• emplate.yml validated with the current myst-templates schema
• Official index command completed successfully for data/typst.yml
• Example exports build with MyST 1.10.1 and Typst 0.15.0 in strict CI mode
• Equations, cross-references, citations, bibliography, figures, tables, proof blocks, exercises, solutions, code, and footnotes are covered by the example