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>

tests/test_trade_service.py

@@ -17,18 +17,6 @@ class FakeSpotClient:
         return {"symbol": kwargs["symbol"], "status": "FILLED", "orderId": 1}
 
 
-class FakeFuturesClient:
-    def __init__(self):
-        self.calls = []
-
-    def new_order(self, **kwargs):
-        self.calls.append(kwargs)
-        return {"symbol": kwargs["symbol"], "status": "FILLED", "orderId": 2}
-
-    def position_risk(self, symbol=None):
-        return [{"symbol": "BTCUSDT", "positionAmt": "-0.02", "notional": "-1200"}]
-
-
 class TradeServiceTestCase(unittest.TestCase):
     def test_spot_market_buy_dry_run_does_not_call_client(self):
         events = []
@@ -66,18 +54,6 @@ class TradeServiceTestCase(unittest.TestCase):
         self.assertEqual(payload["trade"]["status"], "FILLED")
         self.assertEqual(client.calls[0]["timeInForce"], "GTC")
 
-    def test_futures_close_uses_opposite_side(self):
-        with patch.object(trade_service, "audit_event", return_value=None):
-            client = FakeFuturesClient()
-            payload = trade_service.close_futures_position(
-                {"trading": {"dry_run_default": False}},
-                symbol="BTCUSDT",
-                dry_run=False,
-                futures_client=client,
-            )
-        self.assertEqual(payload["trade"]["side"], "BUY")
-        self.assertEqual(client.calls[0]["reduceOnly"], "true")
-
     def test_spot_market_buy_requires_quote(self):
         with patch.object(trade_service, "audit_event", return_value=None):
             with self.assertRaisesRegex(RuntimeError, "requires --quote"):