Replace Swashbuckle attributes with ASP.NET Core equivalents

[Copilot]

Completes the Swashbuckle removal by replacing remaining Swashbuckle annotation attributes in API controllers and request models with native ASP.NET Core equivalents.

Changes

• [SwaggerOperation] → [EndpointName], [EndpointSummary], [EndpointDescription] on all action methods across V1, V2, and V3 controllers
• [SwaggerParameter] → [Description] (System.ComponentModel) on action method parameters
• [SwaggerSchema] → [Description] (System.ComponentModel) on request model properties

Before / After

// Before
[SwaggerOperation(
    OperationId = "GetIttProviders",
    Summary = "Get ITT Providers",
    Description = "Gets the list of ITT providers")]

// After
[EndpointName("GetIttProviders"),
    EndpointSummary("Get ITT Providers"),
    EndpointDescription("Gets the list of ITT providers")]

Guidance to review

34 files changed; all are mechanical attribute substitutions. No logic changes.

Checklist

• Attach to Trello card
• Rebased master
• Cleaned commit history
• Tested by running locally

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