chore(release): bump to v0.2.1 — docs and checker fixes

- Add csv_parse/csv_stringify to checker BUILTINS (false-positive fix)
- Add CSV.md language reference doc
- Add TCP.md and TCP_UDP.md to docs/index.md nav
- Add CSV.md to docs/index.md nav
- Fix TCP.md: add YAML front matter, breadcrumb, footer nav
- Fix CLAUDE.md: add CSV row, correct error-handling row (finally),
  update test coverage table with accurate counts (~1140 total)
- Bump docs/index.md version and test count

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

v0.2.0 — tooling milestone: aether fmt, aether test, aether check, RE…

…PL multi-line

feat: add --version/-V and --help/-h flags; bump version to 0.1.4

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chore: remove macOS x86 release target; clean up docs/EXAMPLES.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chore: bump version to 0.1.3

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

chore: Bump version to 0.1.2

New since 0.1.1:
- Promise.race — resolves with first completing I/O promise
- Promise.allSettled — collect all results without failing fast
- promise.then(callback) — ergonomic on_ready alternative; auto-drains at main() exit
- Test fixes: CWD race condition in clippy regression tests; un-ignore recursion tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>