fix(holdings): env fallback for wallet address

[Zaikon13]

Summary

• clarify the holdings _env_addr helper to document support for both WALLET_ADDRESS and WALLETADDRESS
• confirm that holdings snapshots reuse _env_addr for consistent environment fallback

Testing

• python scripts/cordex_ping.py
• python -c "import main; print('import main OK')"
• PYTHONPATH=. python - <<'PY'
  from core.holdings import holdings_snapshot, get_wallet_snapshot, _env_addr
  from core.pricing import get_price_usd
  import json
  addr = _env_addr()
  print("ENV_ADDR:", addr)
  print("CRO_PRICE:", get_price_usd("CRO"))
  print("RAW_SNAPSHOT:", json.dumps(get_wallet_snapshot(addr), indent=2))
  print("FINAL_SNAPSHOT:", json.dumps(holdings_snapshot(), indent=2))
  PY

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https://chatgpt.com/codex/tasks/task_e_68e53208772883239acd7ce54cc984fe