fix: convert entry_time datetime to timestamp in grace period calculation

TypeError: unsupported operand type(s) for -: 'float' and 'datetime.datetime'

Line 1462: time.time() - guard.entry_time
Fixed to: time.time() - guard.entry_time.timestamp()

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/smart_risk_manager.py

@@ -1459,7 +1459,7 @@ class SmartRiskManager:
                         "normal": 90,
                     }.get(regime, 90)
 
-                    time_since_entry = time.time() - guard.entry_time
+                    time_since_entry = time.time() - guard.entry_time.timestamp()
                     in_grace_period = time_since_entry < grace_period_sec
 
                     # Lower threshold for losses (75%)