Review exercise design: self-contained vs cross-referenced

[braboj]

What

Review all chapter exercises and decide on a consistent approach:

1. Self-contained — each chapter's exercises use their own standalone setup, no dependency on previous chapters
2. Cross-referenced — exercises build on a shared repository (e.g. concepts-lab) that carries state across chapters

Current state

Exercises currently reference concepts-lab from previous chapters but this is inconsistent. Some exercises create new repos (e.g. clone-lab in chapter 4), others assume prior setup.

Trade-offs

Approach	Pros	Cons
Self-contained	Reader can start at any chapter, no prior state needed	Repetitive setup, no progressive complexity
Cross-referenced	Builds naturally, mirrors real workflow	Must read in order, broken if a step is skipped

Decision needed

• Which approach fits the tutorial's beginner audience better?
• If cross-referenced, do we need a "checkpoint" mechanism (e.g. downloadable repo state per chapter)?
• Should exercises link to Learn Git Branching for visualization (Add recommended tools and companion resources page #109)?