Option to hide inline diffs for Edit/Write tool output

Add a setting to suppress the inline diff display that appears in the conversation stream when the Edit or Write tool modifies a file.

The diff dialog (Escape to dismiss) exists, but there's no way to hide the diffs that appear inline during file edits. A setting like "showDiffs": false in settings.json would be useful for users who prefer cleaner output and trust the changes being made.