refactor: Migrate from Minimal API to Controller-based API

Architecture decision change:

  - Previous: Minimal API (DocumentEndpoints.cs) - WRONG approach

  - Required: Controller-based API (per CONTROLLER_ENDPOINTS.md)

New controllers:

  - PdfValidationController:

    - POST /api/pdf/validation/validate

    - Accepts BOTH IFormFile (multipart) AND Base64 JSON

    - Returns PdfValidationResult

  - SwissQrCodeController:

    - POST /api/swissqrcode/extract

    - Accepts BOTH IFormFile (multipart) AND Base64 JSON

    - Returns SwissQrCodeExtractionResult

Controller best practices:

  - Primary constructors (C# 12)

  - Thin controllers (pass request to MediatR directly)

  - No manual mapping (AutoMapper handles domain -> DTO)

  - XML documentation for Swagger

  - [ProducesResponseType] attributes

Deleted:

  - API/Endpoints/v1/DocumentEndpoints.cs (Minimal API)

  - ROADMAP.md (conflicting guidance with CONTROLLER_ENDPOINTS.md)

Result: Controller-based API, dual input support (multipart + JSON)

DocumentOperator.API/Controllers/PdfValidationController.cs

@@ -0,0 +1,79 @@
+using DocumentOperator.Application.Common.DTOs;
+using DocumentOperator.Application.ValidatePdf.Queries;
+using MediatR;
+using Microsoft.AspNetCore.Mvc;
+
+namespace DocumentOperator.API.Controllers;
+
+/// <summary>
+/// PDF validation operations
+/// </summary>
+[ApiController]
+[Route("api/pdf/validation")]
+[Produces("application/json")]
+public class PdfValidationController(IMediator Mediator) : ControllerBase
+{
+    /// <summary>
+    /// Validates a PDF document and returns metadata (multipart/form-data)
+    /// </summary>
+    /// <param name="file">PDF file to validate</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>PDF metadata (page count, file size, PDF version, attachments)</returns>
+    /// <response code="200">PDF is valid, metadata returned</response>
+    /// <response code="400">Invalid PDF or file format</response>
+    /// <response code="500">Internal server error during validation</response>
+    [HttpPost("validate")]
+    [Consumes("multipart/form-data")]
+    [ProducesResponseType(typeof(PdfValidationResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> ValidateFromFile(
+        IFormFile file,
+        CancellationToken cancellationToken)
+    {
+        if (file == null || file.Length == 0)
+        {
+            return BadRequest(new ProblemDetails
+            {
+                Title = "Invalid file",
+                Detail = "File is required and cannot be empty",
+                Status = StatusCodes.Status400BadRequest
+            });
+        }
+
+        // Convert IFormFile to byte array
+        using var memoryStream = new MemoryStream();
+        await file.CopyToAsync(memoryStream, cancellationToken);
+        byte[] pdfBytes = memoryStream.ToArray();
+
+        // Direct pass-through to MediatR
+        var query = new ValidatePdfQuery { PdfBytes = pdfBytes };
+        var result = await Mediator.Send(query, cancellationToken);
+        
+        return Ok(result);
+    }
+
+    /// <summary>
+    /// Validates a PDF document and returns metadata (Base64 JSON)
+    /// </summary>
+    /// <param name="query">PDF as Base64 string</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>PDF metadata (page count, file size, PDF version, attachments)</returns>
+    /// <response code="200">PDF is valid, metadata returned</response>
+    /// <response code="400">Invalid PDF or Base64 format</response>
+    /// <response code="500">Internal server error during validation</response>
+    [HttpPost("validate")]
+    [Consumes("application/json")]
+    [ProducesResponseType(typeof(PdfValidationResult), StatusCodes.Status200OK)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status400BadRequest)]
+    [ProducesResponseType(typeof(ProblemDetails), StatusCodes.Status500InternalServerError)]
+    public async Task<IActionResult> ValidateFromBase64(
+        [FromBody] ValidatePdfQuery query,
+        CancellationToken cancellationToken)
+    {
+        // Direct pass-through to MediatR
+        var result = await Mediator.Send(query, cancellationToken);
+        
+        return Ok(result);
+    }
+}