feat: Add adaptive learning path with self-assessment and lesson quiz skills

Redesign LEARNING-ROADMAP.md with a self-assessment quiz that routes users
to Beginner/Intermediate/Advanced paths instead of a single linear track.
Add two project-local skills:

- self-assessment: comprehensive proficiency quiz (quick or deep mode)
  covering 10 feature areas with per-topic scoring and personalized
  learning paths
- lesson-quiz: per-lesson quiz with 100-question bank (10 per lesson)
  for pre-test, progress check, or mastery verification

Update README.md learning path table with "Recommended For" column and
quiz link. Update .gitignore to track project skills.

.gitignore

@@ -43,8 +43,12 @@ yarn-error.log*
 # Temporary files
 *.tmp
 *.temp
-# Keep .claude/ clean for hand-on section
-.claude/
+# Keep .claude/ clean for hand-on section — except project skills
+.claude/*
+!.claude/skills/
+.claude/skills/*
+!.claude/skills/self-assessment/
+!.claude/skills/lesson-quiz/
 blog-posts/
 
 # EPUB files in root directory