fix(http-server-csharp): resolve declared service namespace

[sophia-ramsey]

This pull request updates the logic for determining the generated C# service namespace in the @typespec/http-server-csharp package. Now, the namespace explicitly declared with @service is always used for the generated C# service namespace, even if an imported or unrelated namespace appears first. The changes also refactor and clarify related code, and add new tests to ensure correct behavior.

Service namespace resolution improvements:

• Added a new function getServiceNamespace in service-discovery.ts to reliably select the namespace declared with @service, falling back to the first non-standard namespace with content if no service is declared.
• Updated getServiceNamespaceName to use the new getServiceNamespace logic, ensuring the correct namespace is used for C# code generation.
• Refactored resolveServiceTypes in service-resolution.ts to use getServiceNamespace instead of the previous custom logic, and updated documentation/comments for clarity. [1] [2]

Testing and documentation:

• Added and updated tests in service-resolution.test.ts to verify that the namespace declared with @service is used, and to cover fallback behavior when no service is declared. [1] [2]
• Added a changelog entry describing the fix and its effect on generated C# service namespaces. (.chronus/changes/http-server-csharp-service-namespace-2026-09-08.md)

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/http-server-csharp@11908

commit: 2094f03

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

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@typespec/http-server-csharp - fix ✏️

Use the namespace declared with @service as the generated C# service namespace, even when an imported or unrelated namespace is encountered first.

[azure-sdk-automation]

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