fix(create-doc): preserve created docs when markdown import fails

[Gujiassh]

Summary

• return a structured partial-success payload when create_doc succeeds but addContentToDocFromMarkdown fails afterward
• preserve the existing hard-failure behavior for true create failures and keep full success responses unchanged
• add focused regressions for workspace/item markdown failures and a thrown append-mutation failure after document creation

Validation

• cd packages/agent-toolkit && npx jest src/core/tools/platform-api-tools/create-doc-tool/create-doc-tool.test.ts --runInBand
• cd packages/agent-toolkit && npx eslint src/core/tools/platform-api-tools/create-doc-tool/create-doc-tool.ts src/core/tools/platform-api-tools/create-doc-tool/create-doc-tool.test.ts --max-warnings=0
• cd packages/agent-toolkit && yarn build

[Gujiassh]

Closing this stale radar PR to keep the queue clean: it has been open for weeks without maintainer response, and I am not going to keep it in the active follow-up set without renewed upstream interest.