feat: project scaffold and build toolchain

[shouze]

Summary

Set up the complete project infrastructure for github-issue-ops.

Tasks

• package.json with Commander, @clack/prompts, picocolors dependencies
• bunfig.toml with test coverage thresholds and preload setup
• tsconfig.json for strict TypeScript / Bun
• knip.json for dead-code detection
• .oxfmtrc.json and .oxlintrc.json formatter/linter config
• .gitignore
• build.ts — Bun.build compile with 6 cross-compile targets + macOS codesign
• install.sh — curl-pipe install script
• entitlements.plist for macOS notarization

Acceptance criteria

• bun install succeeds
• bun run build produces a signed binary at dist/github-issue-ops
• bun run format:check && bun run lint && bun run knip all pass