feat(codegen): sync developer_guides API docs to markdown and swagger

[chyroc]

Summary

• add cmd/coze-api-doc-sync CLI entry to fetch docs from llms.txt section developer_guides
• add internal/apidocsync parser and serializer to:
  • keep only API-like docs that can be serialized
  • write raw markdown into docs/api-markdown/<api>.md
  • generate OpenAPI YAML into docs/api-swagger/<api>.yaml
• add tests for section parsing, API doc parsing, websocket handling, swagger generation, and end-to-end sync flow
• generate and commit current documentation snapshot
  • candidates: 183
  • generated: 126
  • skipped: 57

Validation

• ./scripts/fmt.sh
• ./scripts/lint.sh
• ./scripts/test.sh (Total coverage: 82.6%)
• ./scripts/build.sh
• go run ./cmd/coze-api-doc-sync --output-root docs