Fix OIDC login in desktop: sync apiUrl before startLogin, add app icon

- Config.svelte: call setConfig() before startLogin() so fetchConfig
  uses the user-entered server URL
- Makefile: copy icon.icns into .app bundle Resources
- Info.plist: add CFBundleIconFile entry

cmd/desktop/Info.plist.template

@@ -8,6 +8,8 @@
 	<string>oikos-desktop</string>
 	<key>CFBundleIdentifier</key>
 	<string>com.hubris.oikos-desktop</string>
+	<key>CFBundleIconFile</key>
+	<string>icon</string>
 	<key>CFBundleInfoDictionaryVersion</key>
 	<string>6.0</string>
 	<key>CFBundleName</key>