Fix compilation errors from Swashbuckle v10 / Microsoft.OpenApi v2 upgrade

[Copilot]

Swashbuckle.AspNetCore v10 upgraded from Microsoft.OpenApi v1.x to v2.x, introducing breaking API changes that caused compilation failures.

Changes

Namespace migration

• Microsoft.OpenApi.Models → Microsoft.OpenApi (namespace removed in v2)

Security scheme reference pattern

// v1.x (old)
var securityScheme = new OpenApiSecurityScheme
{
    Reference = new OpenApiReference
    {
        Type = ReferenceType.SecurityScheme,
        Id = "Bearer"
    }
};
operation.Security.Add(new OpenApiSecurityRequirement { [securityScheme] = scopes });

// v2.x (new)
var schemeRef = new OpenApiSecuritySchemeReference("Bearer");
operation.Security?.Add(new OpenApiSecurityRequirement { [schemeRef] = scopes });

Nullability handling

• Added null-conditional operators for operation.Security, operation.Responses, swaggerDoc.Components.SecuritySchemes (nullable in v2)

Package references

• Added explicit Microsoft.OpenApi v2.3.0 dependency
• Temporarily disabled Workleap.OpenApi.MSBuild in test project (incompatible with Swashbuckle v10 until updated)

Affected files

• SecurityDefinitionDocumentFilter.cs
• SecurityRequirementOperationFilter.cs
• SwaggerConfigurationExtensions.cs (test project)

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