feat(content): generate REST and GraphQL client examples

[mysbryce]

Owner-created Content snapshots can now generate client examples through Use this API. Published REST and typed GraphQL calls expose the same eight language targets as ordinary APIs, with an explicit saved-draft choice. The examples require a separate owner-issued query runtime key pinned to the current publication.

Metadata and generation recheck the original owner proof inside the transaction and validate the sealed source. Generation returns text without executing the API, issuing keys, or persisting example input. The dashboard keeps unsupported snapshot editing and publication actions guarded.

Validation:

• Types, production build, formatting, release policy and clean source bundle passed.
• Backend: 423 tests and 10,235 assertions passed.
• Browser: all 84 stories passed locally before two preview-helper readiness fixes; affected browser stories passed afterward. Exact-head CI subsequently passed all 84 stories in 183.47 seconds.
• Full preview gallery: 53 complete receipts and 1,392 images; all 39 new or affected originals reviewed.
• Windows portable: 11 tests and 1,307 assertions passed, including actual compiled GraphQL client-code generation; all 14 portable screenshots reviewed.

This is a source delivery for 0.29.0-alpha.0. It does not publish a new executable or claim that generated examples were compiled in every target language. Live Content reads remain the next separate milestone.

Exact reviewed head: 04e443efcac700a94d2e37aa412da85d373afab4. CI passed all three serialized jobs: 423 backend tests / 10,235 assertions, 84 browser tests, and 11 portable tests / 1,307 assertions.