Format logger source location as file.go:linenum

- Change source location format from separate source and line fields
  to a single source field with format 'file.go:linenum'
- This provides a more concise and standard format for source locations

internal/logger/logger.go

@@ -2,6 +2,7 @@
 package logger
 
 import (
+	"fmt"
 	"log/slog"
 	"os"
 	"path/filepath"
@@ -64,8 +65,7 @@ func getSourceAttrs() []slog.Attr {
 	}
 
 	attrs := []slog.Attr{
-		slog.String("source", file),
-		slog.Int("line", line),
+		slog.String("source", fmt.Sprintf("%s:%d", file, line)),
 	}
 
 	if funcName != "" {