Add recorded contract tests for CloudConvert metadata drift

[bnomei]

Context

SDK behavior can drift when remote metadata changes. Recorded contract tests can protect parsing and response assumptions without depending on live API calls in normal CI.

Tasks

• Capture representative metadata fixtures.
• Add tests for parsing and response-shape assumptions.
• Document how to refresh fixtures intentionally.

Acceptance criteria

• Core metadata parsing is covered by recorded fixtures.
• Normal CI does not require live CloudConvert credentials.
• Fixture refresh process is documented.

Notes

• Generated from the project improvement research pass.
• Keep implementation discussion repository-relative; do not include local machine paths or private setup details.