Render a loading indicator upon first invocation.

Otherwise, no viewport content renders for > 15 s:

#### Environment

1. #### Application

1. ~~~pwsh
winget show ElectronCommunity.ElectronFiddle
~~~

1.

~~~YAML
Installer:
Installer Type: exe
Installer Locale: en-US
Installer Url: https://github.com/electron/fiddle/releases/download/v0.37.2/electron-fiddle-0.37.2-win32-x64-setup.exe
Installer SHA256: d83bfeec2e651e52a152450f5bf9905d1e809161f4c8bac62ff754f8c1afeac7
Release Date: 2025-07-31
Offline Distribution Supported: true
~~~

1. #### OS

1. ~~~pwsh
Get-ComputerInfo | Select-Object -Property @(
'OsName',
'OsOperatingSystemSKU',
'OsVersion',
'OsBuildNumber'
) | Format-List
~~~

1.

~~~YAML
OsName : Microsoft Windows 11 Pro
OsOperatingSystemSKU : 48
OsVersion : 10.0.26120
OsBuildNumber : 26120
~~~