* docs: update document-writer model to Gemini 3 Flash in READMEs
Update model references from gemini-3-pro-preview to gemini-3-flash-preview
and include in available models list for better visibility.
🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)
* chore(document-writer): switch to Gemini 3 Flash model
Update model from gemini-3-pro-preview to gemini-3-flash-preview for
improved performance and cost efficiency.
🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)
Restrict background_task tool access for all spawned subagents (oracle, explore, librarian, frontend-ui-ux-engineer, document-writer, multimodal-looker) to prevent potential infinite recursion and unintended background task creation.
🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)