chore: README + CONTRIBUTING.md + issue templates

[randomm]

What

Discoverability and onboarding. Three small docs.

README.md (~80-120 lines)

1. Title + CI badge (added by issue chore: GitHub repo settings + CI workflow #5)
2. One-paragraph description: Git worktree management plugin for the Pi agent harness. Provides safe create/list/remove of worktrees for parallel agent sessions, with guardrails against the data-loss patterns common in agentic workflows.
3. Status: 0.1.0 — in development
4. Install: pi install npm:@randomm/pi-worktree (once published) or manual copy to ~/.pi/agent/extensions/
5. Configuration: settings.json snippet if applicable
6. Usage: slash commands once feat: slash command handlers — /start, /research, /plan, /work in TypeScript #3 ships (/worktree create, /worktree list, /worktree remove)
7. Safety guarantees: reference the footguns we explicitly guard against (branch-already-checked-out, dirty-remove, prune-before-delete, detached-HEAD, locked-leftover)
8. License: Apache 2.0 — see LICENSE

CONTRIBUTING.md

• Setup: bun install
• Pre-push gates: bunx biome check . && bunx tsc --noEmit && bun test
• Commit format: Conventional Commits with issue scope (e.g. feat(feat: worktree plugin #2):, chore(chore: GitHub repo settings + CI workflow #5):)
• PR rules: include Fixes #N in PR body (not title); pass --base main to gh pr create
• Reference AGENTS.md for the full agent-driven workflow

.github/ISSUE_TEMPLATE/

• bug_report.md
• feature_request.md
• chore.md

Use the same template shapes pi-permissions evolved: title prefix, scope, why, acceptance criteria, out-of-scope, link to AGENTS.md if relevant.

Why

Readme is the front door. CONTRIBUTING tells humans how to send patches. Issue templates keep future issues at the quality bar pi-permissions reached only after several rounds of editing.

Acceptance criteria

• README.md present with all 8 sections
• CONTRIBUTING.md present with setup, gates, commit/PR rules
• Three issue templates under .github/ISSUE_TEMPLATE/
• License section in README says Apache 2.0 and links to LICENSE
• No outdated MIT references anywhere

Out of scope

• Detailed API docs (those live in JSDoc on exported types)
• Tutorial / example projects
• Changelog (defer until 1.0)