Prepare Ruby SDK 3.0.0 with playlist support and generated methods

[wenbinf]

The Ruby client has no playlist write methods and treats successful 201 Created responses as errors. Prepare podcast_api 3.0.0 with five playlist methods, preserving all 25 existing method names, keyword arguments, and HTTParty::Response results.

• Add generated method wrappers, an independent API contract snapshot, and a compact README method reference. The generator and operation registry live in the Listen Notes monorepo; this SDK builds and tests independently.
• Encode path identifiers, separate query and form-body parameters, preserve empty notes/descriptions, and keep client keys and configuration isolated. Accept all 2xx responses, handle 403 with PermissionDeniedError, retain API error details/responses, and correct the User-Agent to podcast-api-ruby.
• Require Ruby 3.3+, update dependencies and the lockfile, add configurable 30-second timeouts, and disable automatic retries and redirects. Remove Travis, unused Mocha, the duplicate Rake file, and the separate example bundle.
• Run offline CI on Ruby 3.3 and 4.0, with a separate integration job against the stateless public mock server.

Validation: 49 offline tests pass on Ruby 3.3.12, 3.4.11, and 4.0.7; 34 public-mock integration tests pass. The gem builds and all 49 offline tests also pass against an isolated installation outside the checkout. Generated methods and README examples cover all 30 operations. Monorepo validation passed 19 generator tests, 10 Django documentation tests, 81 frontend tests, and typechecking; generation is deterministic.

No production API requests or package publication are included. Website Ruby snippets remain gated at the published 1.1.6 release until 3.0.0 is published separately.