docs: add invitation rewards rules

[ai-bankofai]

Summary

• Add Invitation Rewards rules in English and Chinese
• Document 300,000 Credits registration gift, 1% standard rebate, and Coin settlement rules
• Clarify the current 1 Coin = 1,000,000 Credits redemption rate
• Update English and Chinese pricing pages and sidebar navigation
• Bump package version from 1.3.12 to 1.3.13

Verification

• yarn build