chore(release): prepare release 1.18.1 - #11027

This PR prepares the release 1.18.1.

Summary by cubic

Prepares the axios 1.18.1 patch release by bumping the version and finalizing docs across README and localized pages. Removes pre-release tracking notes; no runtime or API changes.

Description

• Summary of changes
  • Bump VERSION in lib/env/data.js and "version" in package.json / package-lock.json to 1.18.1; minor contributors list order tweak.
  • Apply README and /docs/ (en/es/fr/zh) updates: document CancelToken.subscribe/unsubscribe/toAbortSignal, CanceledError (alias Cancel, includes __CANCEL__), AxiosHeaders#set(Iterable) and #toString(), FormData serializer maxDepth and Blob options, and Node env proxy handling via agent proxyEnv/NODE_USE_ENV_PROXY/--use-env-proxy; small example/style cleanups.
  • Remove temporary pre-release notes from PRE_RELEASE_DOCS.md.
• Reasoning
  • Align package metadata and documentation with 1.18.1 behavior and hardening notes.
• Additional context
  • No behavior changes; docs clarify existing runtime and types.

Docs

• README and /docs/ updated; ensure the docs site rebuild/deploy picks up 1.18.1 changes and version references.

Testing

• No tests added or changed; not needed for a version bump and documentation-only updates.

Semantic version impact

• Patch: version bump only, no breaking changes or new features.

^{Written for commit ba8579e. Summary will update on new commits.}