Sync week-01 and week-02 from agentic-research-course blog expansion

Week 1 adaptation of blog/week-01-setup-guide.md:
- Why This Course Starts Here opener (AI landscape, power problem,
  git as safety net)
- How Git Thinks: Three States section with worked staging example
  and the undo button (git restore / git revert)
- GitHub Workflow end-to-end walkthrough: Issue -> Branch -> Commits
  -> PR -> Review -> Merge -> Pull main, run twice for practice
- Linux gh install now uses the official cli.github.com apt repo
  (gh is not in default Ubuntu repos)
- Apple Silicon brew shellenv PATH step
- Faculty benefit corrected: GitHub Team + Copilot Pro (not Pro)
- Retired 'Join Global Campus' button language -> 'Apply'
- Expected output stubs for git log --oneline
- 50-char commit-message rule introduced before the PR workflow uses it

Week 2:
- Drop anthropics/claude-code tap; brew install claude-code resolves
  the cask automatically

Source of truth lives at
https://github.com/OpenScience-Collective/agentic-research-course/blob/main/blog/week-01-setup-guide.md

Author: neuromechanist