fix(eslint-plugin): type public exports with eslint core types

[binjospookie]

What

• Plugin public surface re-typed with ESLint's own types: the default export is ESLint.Plugin & { configs: { recommended: Linter.Config } }, ruleset satisfies Linter.RulesRecord. One internal as unknown as ESLint.Plugin cast bridges the TSESLint↔eslint rule-module signature gap.
• Fixes the type error defineConfig consumers saw on configs.recommended; tseslint.config consumers keep working (their plugins: record accepts Omit<Plugin, "configs"> — pinned as FlatConfig.Plugins[string]).
• New src/index.test-d.ts pins both consumer scenarios, including a literal defineConfig(plugin.configs.recommended) call; vitest typecheck enabled for the package.
• configs uses an explicit annotation instead of satisfies: the inferred type hits TS2883 (non-portable reference into @eslint/core via pnpm path) during dts emit.
• CHANGELOG: entry under Unreleased; version untouched (release pipeline owns it). Root CLAUDE.md now states that rule.

Verified

Build + attw + publint clean; 22 tests passed (20 rule + 2 type), type errors 0; knip + oxlint clean.

Emitted d.mts:

import { ESLint, Linter } from "eslint";
declare const configs: { recommended: Linter.Config };
declare const plugin: ESLint.Plugin & { configs: typeof configs };
export { plugin as default };

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