feat: enhance WelcomeDialog, export dialogs, GitStatusPanel, add CommandPalette, FindReplaceBar, and new converter dialogs

- WelcomeDialog: add quick start, feature showcase, keyboard shortcuts, recent files, version display
- ExportDocxDialog/ExportHtmlDialog/ExportPdfDialog: add header/footer, paper size, margin controls
- GitStatusPanel: full staging/unstaging, discard, commit workflow
- CommandPalette: fuzzy command search with keyboard navigation
- FindReplaceBar: find/replace with regex, case, whole-word options
- New dialogs: BatchMediaConverterDialog, HeaderFooterDialog, PdfEditorDialog, UniversalConverterDialog
- Tests: comprehensive coverage for all new/updated components

tests/component/modals/ExportBatchDialog.test.tsx

@@ -8,12 +8,10 @@ describe('ExportBatchDialog', () => {
     localStorage.clear();
     window.electronAPI = {
       export: {
-        batch: vi
-          .fn()
-          .mockResolvedValue({
-            ok: true,
-            data: { total: 2, succeeded: 2, failed: 0, results: [] },
-          }),
+        batch: vi.fn().mockResolvedValue({
+          ok: true,
+          data: { total: 2, succeeded: 2, failed: 0, results: [] },
+        }),
       },
     } as any;
   });