fix(sdk): expose renderer usage types

[notmike101]

Summary

• export the complete renderer-facing SDK type surface, including sanitized model-request records and subscription targets
• emit NodeNext-compatible declaration imports from every SDK subpath
• make the SDK consumer fixture typecheck the renderer usage API with NodeNext and library checking enabled

Verification

• bun audit
• bun install --frozen-lockfile
• bun run check (30 tests, 131 assertions)
• npm pack ./sdk --dry-run --json
• clean tarball consumer: Node ESM, Node CommonJS, and TypeScript 5.9 NodeNext
• TPS strict typecheck against the corrected renderer entrypoint