Expand week-01 blog: landscape, three-states, GitHub workflow walkthrough (#7)

* Expand week-01 blog with landscape, three-states, GitHub workflow

Adds the walkthrough-style sections the slides teach but the blog skipped:

- 'Why This Course Starts Here' opener: what changed in AI coding, the
  power problem (AI generates code an order of magnitude faster, so it
  produces bugs just as fast without guardrails), and git as the safety
  net that catches AI mistakes.
- New 'How Git Thinks: The Three States' section after the first commit,
  introducing working directory / staging / repository with a hands-on
  example on the reader's own files.
- New 'The GitHub Workflow' section walking the reader through a full
  issue to branch to commit to PR to review to merge loop on their
  my-research-project repo, then repeating it once more so the loop is
  muscle memory before Week 2.

Also:
- Fixed 'Agentic Research Course course' duplication
- SSH now defined as Secure Shell on first use
- Quick Reference expanded with diff --staged, show, branch --show-current,
  checkout; gh issue list, gh pr list, gh pr view --web, gh issue develop
  --checkout
- Updated Week 2 install commands to match v2026.04 (install.sh endpoint,
  Homebrew tap, PowerShell path)
- Linked forward to the Week 2 blog

Closes #6

* Address PR review findings on week-01 blog

Fact-check (CRITICAL):
- Removed 'brew tap anthropics/claude-code'; the cask ships in the
  default homebrew/cask tap, no custom tap needed
- Faculty benefit is GitHub Team (not Pro) plus Copilot Pro
- 'Join Global Campus' -> 'Apply' (branding retired)

Followability (BLOCKER):
- Moved gh auth login guidance after section 4 instead of prompting
  readers to run it before their GitHub account exists
- Linux/WSL gh install now adds the official cli.github.com apt repo
  first (gh is not in default Ubuntu repos); Homebrew fallback noted
- PR push now uses "$(git branch --show-current)" so the
  auto-generated branch name from gh issue develop matches exactly
- macOS section shows the Apple Silicon / Intel brew shellenv PATH
  step that the installer prompts for but readers often miss

Followability (ROUGH):
- LICENSE exercise now clearly labels its contents as a placeholder
  and points at the canonical CC-BY-4.0 legal text
- Merge step leads with 'click Create a merge commit for now' before
  listing the three options as reference
- Section 7 starts with a git-status clean-state check
- Added expected output stubs for git log --oneline (with hash-differs
  caveat) in sections 6 and 9h
- Added an 'undo button' subsection at the end of section 7 fulfilling
  the opener's promise: git restore, git restore --staged, git revert

Style:
- CLI defined on first use ('GitHub's command-line interface (CLI)')
- Dropped HTTPS reference; guide commits to SSH
- 50-character commit-message rule introduced at the end of section 6,
  before section 9 uses it
- Visual loop diagram added to the opener so readers see the
  Issue -> Branch -> Commits -> PR -> Review -> Merge flow twice

Refs #6

Author: neuromechanist