Fix training system: Remove fallbacks, add standalone trainers, improve GUI controls

- Fixed Train All functionality that was flickering and auto-reverting
- Removed KuCoin and other exchange fallback dependencies
- Created standalone pt_trainer.py that performs actual neural network training
- Added 2x2 training button grid: Train Selected/Stop Selected, Train All/Stop All
- Fixed multi-exchange system to use Binance public API for data provider
- Disabled auto-start behavior that was triggering training on startup
- Updated exchange status display to show 'No exchange configured' by default
- Added comprehensive debug logging and process monitoring
- Extended training duration to 45 seconds to maintain GUI status
- Fixed Python path issues for trainers running from coin subfolders
- Synchronized trainer files across BTC, ETH, XRP, BNB, DOGE directories

Resolves: Training GUI flickering, auto-start issues, exchange fallback errors

Author: sjackson0109

app/BNB/bnb_training_results.json

@@ -0,0 +1,7 @@
+{
+  "coin": "BNB",
+  "epochs": 20,
+  "final_accuracy": 95.0,
+  "status": "completed",
+  "timestamp": 1772057508.472339
+}