Document global CLI installation

[JRS1986]

Agentic coding disclosure

• Agent / tool used: Codex
• Model / provider: OpenAI GPT-5
• Human operator: @JRS1986
• Task: Make CodingScaffold easier to install and use from any project folder. Closes Make CodingScaffold easier to install and run globally #80.

What changed

• Files changed: README install docs, Getting Started wiki docs, generated project GETTING_STARTED template, writer regression test, changelog.
• Commands run: uv run ruff check; uv run pytest -q; uv run coding-scaffold context lint --target .; uv run coding-scaffold eval run --target .
• Tests run: uv run ruff check passed; uv run pytest -q passed with 331 tests; context lint passed; eval passed 9/9.
• Tests not run and why: n/a.

Risk surface

• External tools or MCP servers used: GitHub connector attempted issue creation and failed with 403; GitHub CLI created issue, pushed branch, and opened this PR.
• Secrets / data exposure risk: none.
• Network calls made during the session: GitHub issue, branch push, and PR operations only.

Review focus

• Human review focus: confirm uv tool install / pipx install is the desired first-time user path; confirm contributor install instructions remain clear; confirm generated onboarding no longer implies source-repo venv activation.
• Known limitations: no UI work included; the feedback treats GUI as later.
• Reusable knowledge captured: issue Make CodingScaffold easier to install and run globally #80 records the tester feedback.