fix(read_file): use bracket notation for index signature access

packages/core/src/tools/read-file.ts

@@ -237,12 +237,12 @@ export class ReadFileTool extends BaseDeclarativeTool<
     };
 
     if (!isGemini3) {
-      properties.offset = {
+      properties['offset'] = {
         description:
           "Optional: For text files, the 0-based line number to start reading from. Requires 'limit' to be set. Use for paginating through large files.",
         type: 'number',
       };
-      properties.limit = {
+      properties['limit'] = {
         description:
           "Optional: For text files, maximum number of lines to read. Use with 'offset' to paginate through large files. If omitted, reads the entire file (if feasible, up to a default limit).",
         type: 'number',