feat(rotate,delete-pages): Add custom rotation angles and enhance page management UI

- Add TypeScript type definitions for merge and alternate-merge Web Workers
- Implement custom rotation angle input with increment/decrement controls for rotate tool
- Extend delete-pages tool to render page thumbnails for better UX
- Hide number input spin buttons across all number inputs via CSS
- Refactor rotateAll function to accept angle parameter instead of direction multiplier
- Update fileHandler to support delete-pages tool thumbnail rendering
- Improve type safety in alternate-merge logic with proper interface definitions
- Enhance rotate tool UI with custom angle input field and adjustment buttons

src/css/styles.css

@@ -600,4 +600,16 @@ button:disabled,
   mask-image: radial-gradient(ellipse at center, black 40%, transparent 80%);
   -webkit-mask-image: radial-gradient(ellipse at center, black 40%, transparent 80%);
   pointer-events: none;
+}
+
+/* Hide spin buttons for number inputs */
+input[type="number"] {
+  appearance: none;
+  -moz-appearance: textfield; /* Firefox */
+}
+
+input[type="number"]::-webkit-inner-spin-button,
+input[type="number"]::-webkit-outer-spin-button {
+  -webkit-appearance: none; /* Chrome, Safari, Edge */
+  margin: 0;
 }