Support legacy (Datasync/Zumo ≤ v6) clients that expect a relative nextLink #629

Describe the problem

TableController<TEntity>.QueryAsync builds PagedResult.NextLink as a query string only (for example $skip=50&$top=50). Datasync v6 clients (and earlier) resolve nextLink against the host root, not against the table URL. They also send the X-ZUMO-OPTIONS: nextLink=path header to indicate this. A query-only nextLink makes those clients request the wrong URL, so paging fails once a result set exceeds PageSize.

To Reproduce

1. Host a table controller using CommunityToolkit.Datasync.Server with more rows than Options.PageSize.
2. Query it from a v6 client, which sends the header X-ZUMO-OPTIONS: nextLink=path.
3. Inspect nextLink in the response and let the client follow it.
4. The client doesn't request tables/<table>?$skip=..., so paging fails.

Expected behavior

When the request carries X-ZUMO-OPTIONS containing nextLink=path, the server returns nextLink as a path relative to the host root, with no leading slash: tables/<table>?$skip=50&$top=50.

Other clients keep receiving the current query-only format, so there is no breaking change.

Proposed change

In TableController.Query.cs:

• Add IsLegacyClient(HttpRequest). It returns true when the X-ZUMO-OPTIONS header contains nextLink=path (case-insensitive).
• Change CreateNextLink(...) to take a bool legacyClient parameter.
  • If it's false, return the query string (TrimStart('?')) as before.
  • If it's true, return (request.PathBase + request.Path).Value.Trim('/') + queryString.
• Compute legacyClient once in QueryAsync and pass it to CreateNextLink.

What platforms?

• Server:

  • Version of dotnet being used to compile: .NET 10
  • Library versions: CommunityToolkit.Datasync.Server 10.2.0

• Client:

  • Platform: Wpf
  • Version of dotnet being used to compile: .NET 9
  • .NET Runtime Environment: .NET 9
  • Datasync Toolkit NuGet versions: v6 client