docs: Android auto-update page is misplaced; Core docs are outdated

[JusterZhu]

Problem

Two documentation issues identified on the GeneralUpdate-Samples website:

1. Android auto-update page doesn't belong here

/docs/doc/Android auto-update.md documents GeneralUpdate.Maui.Android and GeneralUpdate.Avalonia.Android, which are components from separate repositories:

• GeneralUpdate.Maui
• GeneralUpdate.Avalonia

These components have nothing to do with the GeneralUpdate-Samples repository. The page should be removed from here and maintained in their respective repos.

2. GeneralUpdate.Core docs are outdated

/docs/doc/GeneralUpdate.Core.md hasn't been updated to reflect recent source changes in v10.5.0-beta.2:

• Missing multi-target framework info (net8.0; net10.0)
• Missing AOT/Trim compatibility and JSON source generators
• Auth system was simplified to just Bearer token — missing AuthScheme enum (Hmac, Bearer, ApiKey, Basic)
• Missing cross-platform strategy documentation
• Missing new features (file tree diff, Environments IPC, etc.)

Resolution

PR #85 addresses both issues:

• Removes Android auto-update page from all locations (main + i18n + sidebar)
• Updates GeneralUpdate.Core.md to match the latest source code

Closes via #85