feat: show unseen count in macos dock

Resolves #93

js/src/electron.d.ts

@@ -12,6 +12,9 @@ declare global {
       fetchMetadata: (url: string) => Promise<LinkMetadata | null>;
       openExternal: (url: string) => Promise<void>;
     };
+    electronApp: {
+      setDockBadge: (count: number) => void;
+    };
   }
 }