feat: add chain-spec-tool and usdt-bridge utilities

chain-spec-tool:
- CLI utility for chain spec manipulation and validation
- Used for mainnet chain spec generation and verification

usdt-bridge:
- Custodial bridge for wUSDT token operations
- Handles USDT wrapping/unwrapping between external chains and Asset Hub
- Configuration in bridge_config.json

tools/usdt-bridge/bridge_config.json

@@ -0,0 +1,11 @@
+{
+  "polkadot_rpc": "wss://polkadot-asset-hub-rpc.polkadot.io",
+  "pezkuwi_rpc": "wss://asset-hub-rpc.pezkuwichain.io",
+  "polkadot_usdt_asset_id": 1984,
+  "pezkuwi_wusdt_asset_id": 1000,
+  "min_deposit": 10000000,
+  "min_withdraw": 10000000,
+  "fee_basis_points": 10,
+  "seed_path": "bridge_seed.json",
+  "db_path": "bridge_db.json"
+}