fix(rewrite): route pnpm lint through rtk pnpm

[TechWizard9999]

Description

Fixes rewrite routing for pnpm lint so it no longer gets forced into rtk lint (which can cause ESLint-oriented retry loops in non-ESLint projects).

Related Issue

Closes #665

Changes Made

• updated discovery pattern matching so pnpm lint is recognized by the pnpm rule path
• removed pnpm lint from rtk lint rewrite prefixes
• added rewrite regression tests:
  • pnpm lint -> rtk pnpm lint
  • pnpm lint --fix -> rtk pnpm lint --fix
• added changelog note under Unreleased bug fixes

Files Changed

• src/discover/rules.rs - rewrite/classification adjustments
• src/discover/registry.rs - regression tests for pnpm lint rewrite behavior
• CHANGELOG.md - unreleased bug-fix note for pnpm lint causing issue when ESLint isn't used #665

Testing

• cargo fmt --all --check
• rtk cargo clippy --all-targets (2 pre-existing warnings in untouched files)
• rtk cargo test
• rtk cargo test discover::registry::tests::test_rewrite_pnpm_lint_routes_to_pnpm
• rtk cargo test discover::registry::tests::test_rewrite_pnpm_lint_with_args_routes_to_pnpm
• ./target/debug/rtk rewrite "pnpm lint" -> rtk pnpm lint

Checklist

• Code follows project style guidelines
• Self-review completed
• Documentation updated
• No breaking changes introduced

cc @pszymkowiak for review