Add Brave.BraveOrigin - #161

Adds a task for the stable Brave Origin package (Brave.BraveOrigin). The package was accepted in microsoft/winget-pkgs#466230 and has two versions published, both submitted by hand. The other Brave packages already have tasks, so this fills the gap.

The script follows Brave.Brave: it reads releases/latest from brave/brave-browser, so it only picks up a release once Brave has promoted it, and it takes the release notes from CHANGELOG_DESKTOP.md. Two differences:

• The asset filter matches BraveOriginStandalone instead of BraveBrowserStandalone.
• It sets ReleaseTime and ReleaseNotesUrl from the release. The published manifests link to the release tag, so without this the previous version's URL would carry over.

Validation on Windows 11, PowerShell 7.6.10:

• .\Core\Index.ps1 -Name Brave.BraveOrigin -ThrottleLimit 1 -PassThru: new task, version 157.1.99.56, six installers.
• .\Core\Index.ps1 -Name Brave.BraveOrigin -Force -EnableSubmit -Dry -ThrottleLimit 1: the generated installer and version manifests are identical to the published 157.1.99.56 ones apart from the header comment (same URLs, same hashes, ProductCode: BraveSoftware Brave-Origin). The locale manifest differs only in the release notes line, which now has the same format as Brave.Brave.
• Invoke-ScriptAnalyzer and git diff --check: no findings.

One thing for you to judge: Origin ships from the same release as Brave, so I reused the desktop changelog for the notes. If you would rather leave ReleaseNotes out for Origin, I can drop that block.