chore: update .gitignore to include Cursor IDE files

docs: add changelog entry for 3.0.0 release

docs(v3-step-18): polish 3.x migration guidance

chore(v3-step-18): harden Swift 6.2 concurrency and docs

feat(v3-step-16): implement skills and videos resources

feat(v3-step-15): add webhook verification helpers

feat(v3-step-14): implement evals resources

feat(v3-step-13): implement containers resources

feat(v3-step-09): implement conversations resources

feat(v3-step-08): implement uploads resources

feat(v3-step-07): implement realtime resource surface

feat(v3-step-04): implement responses resources

feat(v3-step-12): implement fine-tuning job resources

feat(v3-step-11): implement batches resources

feat(v3-step-10): implement vector stores resources