Redesign /lessons page layout — reduce information density

[jt14den]

Part of #194.

Feedback (2026-08-04 WG meeting)

The current "stack" of sections on /lessons (src/pages/lessons.astro) reads as too much before you reach the actual catalog:

1. Page intro (eyebrow + title + summary + 2 note paragraphs)
2. "Getting Started with Open Source" section (intro copy + 8-lesson carousel)
3. EducatorToolkit block + a teaching-help note
4. The filter panel + results grid (LessonFilter.tsx)

Goal: cut the number of distinct informational layers before the catalog itself, not just reword what's there.

Depends on / related

• Getting-Started-as-facet issue
• Filter UI simplification issue
• Homepage card deep-linking issue