Fix parameter name mismatch in read_multi_modal tool schema (issue 163)

Change the required parameter name from 'filePath' to 'path' in the
read_multi_modal tool's JSON schema to match the property definition
and the ReadFileToolParams struct field name.

tools/read_multi_modal.cpp

@@ -19,7 +19,7 @@ Tool make_read_multi_modal() {
                     {"description", "Absolute or relative path to multi modal file to read"}
                 }},
             }},
-            {"required", {"filePath"}}
+            {"required", {"path"}}
         },
         .execute = create_tool_execute<ReadFileToolParams>([](const ReadFileToolParams& params) -> Content {
             std::vector<ContentPart> ret{};