Add debug logging and optimize SQLite performance

- Add debug logging for goroutines and memory usage (enabled via DEBUG=routewatch)
- Increase SQLite connection pool from 1 to 10 connections for better concurrency
- Optimize SQLite pragmas for balanced performance and safety
- Add proper shutdown handling for peering handler
- Define constants to avoid magic numbers in code

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

internal/routewatch/app.go

@@ -139,6 +139,10 @@ func (rw *RouteWatch) Shutdown() {
 		rw.logger.Info("Flushing prefix handler")
 		rw.prefixHandler.Stop()
 	}
+	if rw.peeringHandler != nil {
+		rw.logger.Info("Flushing peering handler")
+		rw.peeringHandler.Stop()
+	}
 
 	// Stop services
 	rw.streamer.Stop()