docs: add AXe and IDB third-party license notices

[cameroncooke]

Summary

• mirror the AXe license-notice approach by adding a top-level THIRD_PARTY_LICENSES file
• include attribution for bundled AXe and Meta's IDB (MIT)
• link the notices file from the README license section
• add an Unreleased changelog entry

Why

XcodeBuildMCP redistributes AXe artifacts, so explicit third-party attribution should live in this repo as well.

Validation

• pre-commit checks ran during commit:
  • npm run format:check
  • npm run lint
  • npm run build
  • npm run docs:check

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/xcodebuildmcp@258

commit: 52aac04