refactor: Move DTOs from Domain to Application layer

- Move PdfMetadata, PdfAMetadata from Domain.Models.ValueObjects to Application.Common.DTOs
- Move AttachmentInfo, AttachmentMetadata from Domain.Models.ValueObjects to Application.Common.DTOs
- Reason: DTOs belong in Application layer, Domain should have zero external dependencies (Clean Architecture)

DocumentOperator.Domain/Models/ValueObjects/PdfAMetadata.cs

@@ -1,47 +0,0 @@
-namespace DocumentOperator.Domain.Models.ValueObjects;
-
-/// <summary>
-/// PDF/A validation metadata including conformance level and validation errors/warnings
-/// </summary>
-public sealed class PdfAMetadata
-{
-    public bool IsValid { get; }
-    public string PdfVersion { get; }
-    public int PageCount { get; }
-    public long FileSizeBytes { get; }
-    public bool Encrypted { get; }
-    public string? PdfAVersion { get; }
-    public bool PdfACompliant { get; }
-    public IReadOnlyList<string> Errors { get; }
-    public IReadOnlyList<string> Warnings { get; }
-
-    // Computed property
-    public double FileSizeMB => FileSizeBytes / 1024.0 / 1024.0;
-
-    public PdfAMetadata(
-        bool isValid,
-        string pdfVersion,
-        int pageCount,
-        long fileSizeBytes,
-        bool encrypted,
-        string? pdfaVersion,
-        bool pdfaCompliant,
-        IReadOnlyList<string> errors,
-        IReadOnlyList<string> warnings)
-    {
-        IsValid = isValid;
-        PdfVersion = pdfVersion;
-        PageCount = pageCount;
-        FileSizeBytes = fileSizeBytes;
-        Encrypted = encrypted;
-        PdfAVersion = pdfaVersion;
-        PdfACompliant = pdfaCompliant;
-        Errors = errors;
-        Warnings = warnings;
-    }
-
-    public override string ToString()
-    {
-        return $"PDF/A: {PdfAVersion ?? "None"}, {PageCount} pages, {FileSizeMB:F2} MB, Compliant: {PdfACompliant}";
-    }
-}

DocumentOperator.Domain/Models/ValueObjects/PdfMetadata.cs

@@ -1,32 +0,0 @@
-namespace DocumentOperator.Domain.Models.ValueObjects;
-
-public sealed class PdfMetadata
-{
-    public int PageCount { get; }
-    public long FileSizeBytes { get; }
-    public string PdfVersion { get; }
-    public bool HasAttachments { get; }
-    public int AttachmentCount { get; }
-
-    // Computed Property (berechnet aus FileSizeBytes)
-    public double FileSizeMB => FileSizeBytes / 1024.0 / 1024.0;
-
-    public PdfMetadata(
-        int pageCount,
-        long fileSizeBytes,
-        string pdfVersion,
-        bool hasAttachments,
-        int attachmentCount)
-    {
-        PageCount = pageCount;
-        FileSizeBytes = fileSizeBytes;
-        PdfVersion = pdfVersion;
-        HasAttachments = hasAttachments;
-        AttachmentCount = attachmentCount;
-    }
-
-    public override string ToString()
-    {
-        return $"PDF: {PageCount} pages, {FileSizeMB:F2} MB, Version {PdfVersion}, Attachments: {AttachmentCount}";
-    }
-}