docs: in-depth/client/index.md says ".NET 9" but README says ".NET 10.x or later" #545

Summary

docs/in-depth/client/index.md line 3 says:

This guide shows you how to perform common scenarios using the Datasync Community Toolkit. Use the client library in any .NET 9 application, including AvaloniaUI, MAUI, Uno Platform, WinUI, and WPF applications.

But README.md states:

Client: .NET clients using .NET 10.x or later

Found while confirming PR #533 doesn't need any Uno-version-related docs updates (it doesn't - docs/ never mentions a specific Uno Platform version anywhere) - this is an unrelated, pre-existing inconsistency spotted along the way.

Suggested fix

Update docs/in-depth/client/index.md to say ".NET 10.x or later" (or whatever the current minimum supported client .NET version is) to match README.md, and check the rest of docs/in-depth/client/ for any other stale ".NET 9" references while in there.