GitLab

* Improve target docs and helper messaging

  Commit Message:

  - add SUPPORTED_TARGETS metadata and expose describe_supported_targets()
  - relax target validation to accept option suffixes and upgrade error messages
  - document target usage and compute capability mapping in docs/get_started/targets.md
  - note preference for string targets when caching and link the new guide in docs/index.md

* remove american english spelling