Remove dead code: legacy config fields, unused helpers/imports, stray files

- Delete test_ws_dual.py (standalone probe, unused) and a stale tracked log
- config.py: drop MarketSession enum, is_jpy_pair, candle_buffer_seconds,
  and the never-read legacy SignalConfig/XauStrategyConfig fields
- data_provider.py: drop uncalled get_latest_price/get_spread_estimate
- Remove unused imports (engine, telegram_bot, main, news_engine)
- test_all.py: drop/trim the corresponding defaults assertions (199 tests)
- CLAUDE.md updated to match

Zero behavior change: no production code read any removed field
(verified reference-by-reference); suite green at 199/199.

Claude-Session: https://claude.ai/code/session_01VPNF37MP9Kuv62B1VBrZ1b

news_engine.py

@@ -14,7 +14,7 @@ import threading
 import time
 import xml.etree.ElementTree as ET
 from dataclasses import dataclass, field
-from datetime import datetime, timedelta, timezone
+from datetime import datetime, timezone
 from typing import Dict, List, Optional, Tuple
 
 import requests