feat: Clean up dead code within remaining files

- detect.py: remove unused imports (time, hashlib, log2)
- bitcoin_rpc.py: remove __main__ test block, unused CLI/SIGNET_ARGS vars,
  and unused functions (fund_wallet, wait_for_mempool_empty, decode_psbt,
  decode_raw_tx), remove unused time import
- VulnerabilityBadge.jsx: verified clean, no UtxoCard references
- WalletResource.java: already cleaned in prior commit

backend/script/detect.py

@@ -20,11 +20,8 @@ Usage:
 import sys
 import os
 import json
-import time
-import hashlib
 import argparse
 from collections import defaultdict
-from math import log2
 
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 from bitcoin_rpc import cli, get_tx