feat(deeplink): add support for apt:// protocol handling

- Register apt protocol handler in Electron main process
- Add x-scheme-handler/apt MIME type to electron-builder config
- Update desktop entry to include apt MIME type support
- apt://pkgname links are now converted to spk://search/pkgname

refs #IJTPFP

electron-builder.yml

@@ -26,6 +26,7 @@ linux:
       Categories: "System;"
   mimeTypes:
     - "x-scheme-handler/spk"
+    - "x-scheme-handler/apt"
   target:
     - "AppImage"
     - "deb"