- sitemap.xml: 217 URLs (205 lessons + 10 topics + 2 static)
- build_lesson_pages.py: unique slugs with hash on collision
- Generated topic pages for all domains in lessons.json
- Removed stale manual sitemap entries (feishu, fanuc were 404)

Signed-off-by: Ikalus1988 <sheldonisspark@gmail.com>