chore(kuru): add cbBTC, AUSD, and XAUt0 USDC markets

[dak-agent]

Adds three new Kuru markets to the mainnet entry (mainnet/kuru.jsonc), following the existing Market-<PAIR> naming convention:

Market	Address
Market-cbBTC/USDC	0x40c49f171202f91ff5d2fae34c22dd2bfdd22af0
Market-AUSD/USDC	0x699abc15308156e9a3ab89ec7387e9cfe1c86a3b
Market-XAUt0/USDC	0x851145eaefdc37956b08da829fa31722199f3f07

Requested by Keone (Slack). Validated locally with python scripts/validate_protocol.py --network mainnet (passes; no invalid addresses, duplicates, or canonical-contract collisions).

[github-actions]

Contract Verification Results

Changed Files

• mainnet/kuru.jsonc

Verification Output

Verifying 1 protocol file(s)...

  ✓ Kuru (15 addresses)

================================================================================
                         CONTRACT VERIFICATION RESULTS                          
================================================================================

✓ Kuru (kuru.jsonc)

================================================================================
                                    SUMMARY                                     
================================================================================
  Files Processed:     1
  Addresses Checked:   15
  ✓ Verified:          15
  ✗ Not Verified:      0

  All contracts verified successfully!
================================================================================

---

_{Workflow run: Verify PR Contracts}