Important

Add isFree flag to model schema and update logic to set usage cost to zero for free models.

• Behavior:
  • Add isFree flag to modelInfoSchema in model.ts to indicate free models.
  • Update getRooModels in fetchers/roo.ts to set isFree based on model tags.
  • Modify RooHandler in roo.ts to set totalCost to 0 for free models.
• Misc:
  • Add comments in roo.ts to explain the handling of free models.

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