feat: Add node integration, TRP-gated auth, CIP-8 verification

- Node integration endpoints:
  - GET /v1/address/{address}/utxos - query UTxOs directly from node
  - POST /v1/tx/submit - submit signed transactions
  - GET /v1/protocol-params - current epoch protocol parameters

- TRP-gated permissionless API keys:
  - POST /v1/auth/challenge - get nonce for wallet signing
  - POST /v1/auth/verify - verify CIP-8 signature, issue key based on TRP balance
  - POST /v1/auth/refresh - re-check TRP balance and update tier
  - Background task: hourly tier refresh for all TRP-gated keys

- Tier thresholds: 50+ TRP = standard, 500+ TRP = elevated
- TX submit rate limits: anonymous=blocked, standard=2/min, elevated=10/min
- Added pycardano, cbor2, PyNaCl dependencies
- Updated Dockerfile with cardano-cli binary

requirements.txt

@@ -4,3 +4,6 @@ asyncpg==0.30.0
 redis==5.0.0
 pydantic==2.9.0
 python-dotenv==1.0.0
+pycardano==0.11.0
+cbor2==5.6.0
+PyNaCl==1.5.0