- Add handleExportWithoutHistory function for fetching current diagram state without saving to history
- Update onFetchChart to accept saveToHistory parameter (defaults to true)
- edit_diagram tool now fetches with saveToHistory=false since it only needs the current state
- Only the initial form submission saves to history as intended
- Add save button in chat input area with download icon
- Create SaveDialog component for filename input
- Export current diagram as .drawio file format
- Support custom filename with default timestamp-based name
Closes#53
When sending a message, the history was being added twice because:
1. handleExport() triggers exportDiagram() which adds to history
2. AI responds and loadDiagram() is called, which internally triggers
another export event in DrawIO, adding a duplicate entry
Added expectHistoryExportRef flag to track user-initiated exports and
only add to history when the export was explicitly requested.
