docs: README, CONTRIBUTING, CLAUDE.md, CHANGELOG seed, TASKS.md

[constk]

Problem

Users land on README first; without a polished landing page (what / why / quickstart / architecture / badges), the template doesn't communicate its value.

Proposed solution

Write README.md with: 1-paragraph value prop ("prod-quality LLM-driven coding harness"), feature list (harness mechanics enumerated), quickstart (gh repo create --template constk/harness-python-react, uv sync, just check, docker compose up), architecture diagram, badges (CI, coverage, license, Python, Node, React versions). Write CONTRIBUTING.md (branching, commit style, PR flow). Write CLAUDE.md (harness-first project instructions for Claude Code). Seed CHANGELOG.md for release-drafter. Write docs/TASKS.md analogue documenting this template's bootstrap phases.

Acceptance criteria

• README covers what / why / quickstart / architecture / badges.
• CONTRIBUTING.md cites the 7-prefix commit schema.
• CLAUDE.md explicitly tells Claude Code to read docs/HARNESS.md first.
• Badges resolve to live data (CI status, license, etc.).

Priority rationale

High: this is the portfolio surface.

Depends on

#25

[constk]

Merged in PR #61.