refactor: remove all futures-related capabilities

Delete USDT-M futures support since the user's Binance API key does not
support futures trading. This simplifies the CLI to spot-only:

- Remove futures client wrapper (um_futures_client.py)
- Remove futures trade commands and close position logic
- Simplify account service to spot-only (no market_type field)
- Remove futures references from opportunity service
- Update README and tests to reflect spot-only architecture
- Bump version to 2.0.7

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/coinhunter/runtime.py

@@ -199,10 +199,8 @@ def _render_tui(payload: Any) -> None:
         overview = payload.get("overview", {})
         print(f"\n{_BOLD}{_CYAN} ACCOUNT OVERVIEW {_RESET}")
         print(f"  Total Equity: {_GREEN}{_fmt_number(overview.get('total_equity_usdt', 0))} USDT{_RESET}")
-        print(f"  Spot Equity:  {_fmt_number(overview.get('spot_equity_usdt', 0))} USDT")
-        print(f"  Futures Equity: {_fmt_number(overview.get('futures_equity_usdt', 0))} USDT")
         print(f"  Spot Assets:  {_fmt_number(overview.get('spot_asset_count', 0))}")
-        print(f"  Futures Positions: {_fmt_number(overview.get('futures_position_count', 0))}")
+        print(f"  Positions: {_fmt_number(overview.get('spot_position_count', 0))}")
         if payload.get("balances"):
             print()
             _render_tui({"balances": payload["balances"]})