Remove dead store-and-forward and message aggregation code (#438)

- Remove completely unused message aggregation system (100% dead code)
- Remove broken store-and-forward implementation that only worked for relayed messages to offline favorites
- Update documentation to reflect actual functionality
- Net reduction of 312 lines of unmaintained code

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Utils/BatteryOptimizer.swift

@@ -56,15 +56,6 @@ enum PowerMode {
         case .ultraLowPower: return 30.0 // Advertise every 30 seconds
         }
     }
-    
-    var messageAggregationWindow: TimeInterval {
-        switch self {
-        case .performance: return 0.05  // 50ms
-        case .balanced: return 0.1      // 100ms
-        case .powerSaver: return 0.3    // 300ms
-        case .ultraLowPower: return 0.5 // 500ms
-        }
-    }
 }
 
 class BatteryOptimizer {