feat(pdf-tools): add alternate merge tool for mixing pdf pages

Implement new tool that allows users to combine PDFs by alternating pages from each document. Includes UI components, logic for processing, and test coverage.

- Add new tool to configuration arrays and categories
- Create UI with drag-and-drop file ordering
- Implement core logic for alternating pages
- Add comprehensive unit tests

src/tests/pdf-tools.test.ts

@@ -58,7 +58,7 @@ describe('Tool Configuration Arrays', () => {
     });
 
     it('should have the correct number of tools', () => {
-      expect(multiFileTools).toHaveLength(10);
+      expect(multiFileTools).toHaveLength(11);
     });
 
     it('should not contain any duplicate tools', () => {