Fix conflicting AddLinkedResource method signatures

[Copilot]

The interface IAttachmentCollection defined two overloads of AddLinkedResource for byte arrays that conflicted due to having the same parameter types in different order, causing a compilation error.

Changes:

• Removed obsolete AddLinkedResource(byte[], string fileName, string contentType, string contentId) signature from interface
• Kept preferred signature AddLinkedResource(byte[], string contentType, string contentId, string? fileName = null)
• Updated implementation in AttachmentCollection.cs to match new signature
• Updated test callers to use new parameter order

API Change:

// Old (removed):
.AddLinkedResource(imageBytes, fileName, contentType, contentId)

// New:
.AddLinkedResource(imageBytes, contentType, contentId, fileName)

The new signature follows the pattern established by other AddLinkedResource overloads (contentType before contentId) and makes fileName optional.

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