feat(icon): replace the template's Avalonia logo with a YKanBan icon

The window, the Windows executable and the macOS bundle now use a
placeholder kanban icon (three columns of cards) instead of the template's
avalonia-logo.ico, which had no icon at all on macOS.

packaging/macos/Info.plist

@@ -8,6 +8,8 @@
     <string>YKanBan</string>
     <key>CFBundleIdentifier</key>
     <string>cn.blumia.code.yyc12345.ykanban</string>
+    <key>CFBundleIconFile</key>
+    <string>ykanban.icns</string>
     <key>CFBundleExecutable</key>
     <string>YKanBan</string>
     <key>CFBundlePackageType</key>