fix(http-server-csharp): don't emit auth scheme models and fix enum member rendering

[timotheeguerin]

Fixes #11449

Problem

When a spec applies @useAuth(...) with a named auth scheme model (e.g. model AzureApiKeyAuthentication is ApiKeyAuth<ApiKeyLocation.header, "Ocp-Apim-Subscription-Key">), @typespec/http-server-csharp generated a C# model class for the auth scheme. That class:

1. Should not be generated at all — auth scheme models are protocol/security metadata, not payloads. The OpenAPI3 emitter emits them under components.securitySchemes, never as schemas.
2. Failed to compile — its enum-member-typed properties (type: AuthType.apiKey, in: Location) rendered as <Unresolved Symbol: refkey[...]>, producing C# errors like The name 'refkey' does not exist in the current context.

These are two independent bugs.

Root causes

• Auth models emitted: getServiceModels (service-resolution.ts) collected every named model in the service namespace, including @useAuth scheme models.
• Unresolved symbol: the server TypeExpression had no EnumMember case, so it fell through to the emitter-framework component which emits efRefkey(enumMember). Regular Enum members never register a member refkey (only union-enums do), so the reference was unresolved.

Fix

• service-resolution.ts — collect auth scheme models via getAllHttpServices + resolveAuthentication (the same source the OpenAPI3 emitter uses) and exclude them from model discovery.
• type-expression.tsx — add an EnumMember case that renders the parent enum type (kind: Color.red → Color), with a primitive-type fallback for std-lib enums (e.g. TypeSpec.Http.AuthType) that are never emitted.

Tests

Added toRenderTo component tests (no additions to generation.test.ts):

• models.test.tsx — an @useAuth scheme model is excluded from resolveServiceTypes(...).models and not rendered.
• type-expression.test.tsx — an enum-member property renders as its parent enum; a std-lib enum member falls back to string.

Full package suite passes (206 tests). Changeset included.

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commit: 33b5bfd

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-server-csharp

Show changes

@typespec/http-server-csharp - fix ✏️

Do not generate C# model classes for authentication scheme models (e.g. models referenced by @useAuth), aligning with the OpenAPI3 emitter which treats them as security metadata. Also fix a property typed as an enum member (e.g. kind: Color.red) rendering as an unresolved symbol; it now uses the parent enum type.

[azure-sdk-automation]

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[timotheeguerin]

@copilot fix spellcheck