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

src/main/utils/paths.js

@@ -29,7 +29,7 @@ function validatePath(filePath) {
   let resolved;
   try {
     resolved = path.resolve(filePath);
-  } catch (err) {
+  } catch (_err) {
     return { valid: false, resolved: '', error: 'Invalid path format' };
   }
 
@@ -63,7 +63,7 @@ function resolveWritablePath(filePath) {
   let resolved;
   try {
     resolved = path.normalize(path.resolve(filePath));
-  } catch (err) {
+  } catch (_err2) {
     return { valid: false, resolved: '', error: 'Invalid path format' };
   }