docs: Add CLAUDE.md

[kubode]

Why

I want the assumptions required to work in this repository to live in the repository itself, so that coding agents (and new contributors) don't have to rediscover them.

This monorepo has several conventions that are not visible from any single file:

• The packages form a dependency layer (prettier-config / plugins → configs → frolint), so a change in a lower layer ripples upward.
• The config packages' tests are snapshots of the resolved ESLint config, not of the source. A rule change always requires yarn test:update, and the snapshot diff is the actual review surface.
• yarn build must run before testing frolint and eslint-plugin-wantedly, because main / bin point at the compiled lib/.
• The scaffdog template for new rules still emits Linter#defineRule and legacy RuleTester parser options, both dropped in ESLint 9, so generated code needs manual fixing.
• Releases go through Changesets, not manual version bumps.

What

• Add CLAUDE.md at the repository root, covering commands, the release flow, and the architecture of the six packages.
• Generated with /init in Claude Code, then rewritten against the actual source (rule files, config entry points, DefaultCommand, CI and release workflows) so every statement is backed by code in this repository.

No production code or published package is touched.

🤖 Generated with Claude Code