feat: upgrade marked to v17 with marked-highlight extension

- Update marked from ^16.2.1 to ^17.0.3
- Add marked-highlight ^2.2.3 for syntax highlighting support
- Replace deprecated marked.setOptions() with marked.use() in renderer.js
- Extract highlight config into markedHighlight() extension (required in v17)
- Update test mock to reflect new API (use instead of setOptions)

package.json

@@ -60,7 +60,8 @@
     "electron-store": "^10.1.0",
     "highlight.js": "^11.11.1",
     "html2pdf.js": "^0.10.1",
-    "marked": "^16.2.1",
+    "marked": "^17.0.3",
+    "marked-highlight": "^2.2.3",
     "pdf-lib": "^1.17.1",
     "pdfjs-dist": "^3.11.174",
     "pdfkit": "^0.14.0",