feat(toolbar): add column visibility and CSV export features

- Implemented GridToolbar component for column visibility and CSV export
- Added ColumnVisibilityMenu for toggling column visibility
- Created exportToCsv function for exporting visible data to CSV
- Updated Griddy component to integrate toolbar functionality
- Enhanced documentation with examples for new features

src/Griddy/core/GriddyStore.ts

@@ -22,6 +22,7 @@ export interface GriddyStoreState extends GriddyUIState {
   columnFilters?: ColumnFiltersState
   columns?: GriddyColumn<any>[]
   data?: any[]
+  exportFilename?: string
   dataAdapter?: DataAdapter<any>
   dataCount?: number
   getRowId?: (row: any, index: number) => string
@@ -42,6 +43,7 @@ export interface GriddyStoreState extends GriddyUIState {
   search?: SearchConfig
 
   selection?: SelectionConfig
+  showToolbar?: boolean
   setScrollRef: (el: HTMLDivElement | null) => void
   // ─── Internal ref setters ───
   setTable: (table: Table<any>) => void