Bring TypeScript client emission to parity

[meoyawn]

Closes #7

Summary

• derive valid TypeScript symbols from arbitrary OpenAPI operation IDs
• honor document and operation servers while keeping explicit base URL overrides authoritative
• emit raw BodyInit and ordered multipart/related request bodies from the OpenAPI contract
• validate multipart part media types and reject unsupported request-body shapes during generation
• update TypeScript goldens and client-generation documentation

Verification

• task check
• strict TypeScript 5.9.2 typecheck of the generated dotted-operation client
• Vitest runtime coverage for server precedence, query parameters, multipart ordering, content types, complete media bytes, and explicit overrides