fix: Correct function name check_existing_position to check_existing_positions

Fixed NameError in enhanced trading check:
- check_existing_position() does not exist
- Correct function is check_existing_positions() (with 's')

Fixed in:
- activate_enhanced_scoring.py
- Notebook cells 84 and 89

Error resolved: NameError: name 'check_existing_position' is not defined

dynamic_thresholds.json

@@ -1,5 +1,5 @@
 {
-  "timestamp": "2026-01-21T13:09:03.667837",
+  "timestamp": "2026-01-21T13:24:31.582409",
   "session_thresholds": {
     "asian": 60,
     "ny": 60,