[sb123sb123]

Summary

Keep the existing runtime error text and exit status, then add an actionable hint for model lookup errors, quota and rate-limit responses, service 5xx errors, and connection refused on a localhost or loopback endpoint. Preserve 401 handling and leave other errors without a hint.

Related issue

Closes #16

Type of change

• Bug fix (fixes a problem without changing intended behavior)
• New feature (adds functionality without breaking existing usage)
• Breaking change (changes existing flags, environment variables, output or exit codes)
• Documentation only
• Tests, CI, build or refactoring (no user facing change)

Checklist

• I added or updated tests for this change.
• make test and make lint pass locally.
• I added an entry under ## [Unreleased] in CHANGELOG.md for user facing changes.
• I updated the docs (README.md, aiterm -h help text) where needed.
• My commit and pull request title follow Conventional Commits.

Local Go tests and lint were not run; only about 62 MiB was free on the designated G: workspace.