Prep Martha Week 2 materials (Bun + Astro)

## Must complete by Monday April 6 sync - [x] Write Bun install guide — `guide-bun-install.md` - [x] Write Astro quick-start steps — `guide-astro-quickstart.md` - [ ] Create a reference Astro project that shows the component pattern Martha should follow (optional but helpful) - [ ] Review Martha's Penpot design for optimified.com from Week 1 — give feedback at Monday sync