Adjust concurrent handlers and query threshold

- Set concurrent handlers back to 100 (from 200)
- Set slow query threshold to 50ms (from 10ms)

These values provide a good balance between throughput and
system resource usage.

internal/database/slowquery.go

@@ -7,7 +7,7 @@ import (
 	"time"
 )
 
-const slowQueryThreshold = 100 * time.Millisecond
+const slowQueryThreshold = 50 * time.Millisecond
 
 // logSlowQuery logs queries that take longer than slowQueryThreshold
 func logSlowQuery(logger *slog.Logger, query string, start time.Time) {