Add week-02 blog: Claude Code setup walkthrough (#5)

* Add week-02 blog: Claude Code setup walkthrough

Ports the week-02 source from osc-docs into the course repo as the
canonical plain-markdown blog, then expands it into a full walkthrough:
narrative opener, before/after CLAUDE.md example, starter .context/
file contents, new Prompting for Research section, and the HBN
practicum preview threading weeks 3 through 9.

Source of truth now lives here; the osc-docs copy becomes a MkDocs
adaptation done as follow-up work.

Closes #4

* Address PR review findings on week-02 blog

Fact-check (CRITICAL):
- Auto mode flag is --permission-mode auto, not --enable-auto-mode
- Auto mode is in the Shift+Tab cycle; available on Max/Team/Enterprise/API, not Pro
- Accept Edits auto-approves touch and rmdir too
- Plan mode is read-only; no arbitrary shell commands
- Nonprofit eligibility is 501(c)(3), not 'university'; 20 is a Goodstack
  threshold, not an eligibility cap

Install followability (BLOCKER):
- Homebrew install now taps anthropics/claude-code first
- Linux section notes curl may need 'sudo apt install curl' (WSL minimal)
- claude auth status clarified as shell-level, not inside the REPL
- Plugin install uses the real /plugin marketplace add + /plugin install
  slash-command flow
- Ctrl+G warns about the vi fallback when EDITOR is unset
- Shift+Tab 'twice' qualified so the count depends on starting mode
- /clear gets a one-line gloss on first mention

Style:
- First-use expansions for CLI, API, PR, MCP, RSI, MNE-Python, HBN
- Week 1 reminder spells out what was covered
- Lean CLAUDE.md example now points at .context/plan.md and
  .context/scratch_history.md so the before/after and the .context/
  section form one coherent worked example
- Bundled skills table now referenced in section 9 body
- Savings not saving

Refs #4

Author: neuromechanist