Honor client preference order in WebSocket sub-protocol negotiation

[glen-84]

Summary

• WebSocketConnection.TryAcceptConnection walks the client's Sec-WebSocket-Protocol list in the order it was sent and accepts the first sub-protocol that has a registered handler, so a client offering graphql-transport-ws, graphql-ws is answered with graphql-transport-ws. Handler registration and the ProtocolError close for unsupported protocols are unchanged.
• The HTTP transport docs describe preference-ordered negotiation and the 1002 close.

Test plan

• New WebSocketConnectionTests cover both preference orders, an unsupported protocol listed ahead of a supported one, each protocol offered alone, and unsupported-only offers closing with ProtocolError.
• HotChocolate.AspNetCore.Tests and HotChocolate.Transport.Sockets.Client.Tests pass on net10.0.

[Copilot]

Pull request overview

This PR updates Hot Chocolate’s WebSocket sub-protocol negotiation to honor the client’s Sec-WebSocket-Protocol preference order, selecting the first client-offered protocol that has a registered handler. It also aligns the documentation and adds targeted tests to validate the negotiation behavior and the 1002 (ProtocolError) close for unsupported protocol offers.

Changes:

• Update WebSocketConnection.TryAcceptConnection to iterate requested sub-protocols in client-specified order and accept the first supported one.
• Add new WebSocketConnectionTests covering preference ordering and unsupported-protocol close behavior.
• Update the HTTP transport documentation to describe preference-ordered negotiation and the 1002 close.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
website/content/docs/hotchocolate/server/http-transport.md	Documents preference-ordered Sec-WebSocket-Protocol negotiation and 1002 close behavior.
src/HotChocolate/AspNetCore/test/AspNetCore.Tests/Subscriptions/WebSocketConnectionTests.cs	Adds tests validating negotiation order and ProtocolError close when no offered protocols are supported.
src/HotChocolate/AspNetCore/src/AspNetCore.Pipeline/Subscriptions/WebSocketConnection.cs	Implements client-preference-ordered protocol selection by scanning requested protocols first.

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[github-actions]

Patch coverage

100.0% of changed lines covered (15/15)

File	Covered	Changed	Patch %
…/src/AspNetCore.Pipeline/Subscriptions/WebSocketConnection.cs	15	15	100.0% 🟢

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Project coverage: 56.3% (265086/470693 lines)