Added the catalogue models and seed to support phase 3 of the POC prototype in the Persistence package.

Packages/Persistence/Sources/Internal/Models/MessageRecord.swift

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+import FluentKit
+import Foundation
+
+/// A FluentKit model of a single `messages` row: something said, an offer made, or an event stamped into a conversation.
+final class MessageRecord: Model, @unchecked Sendable {
+
+    // MARK: Properties
+
+    static let schema = "messages"
+
+    @ID(key: .id)
+    var id: UUID?
+
+    @Parent(key: "conversation_id")
+    var conversation: ConversationRecord
+
+    /// Who wrote the message, made the offer, or caused the event.
+    @Parent(key: "sender_id")
+    var sender: UserRecord
+
+    @Field(key: "kind")
+    var kind: String
+
+    @Field(key: "body")
+    var body: String
+
+    @OptionalParent(key: "offer_id")
+    var offer: OfferRecord?
+
+    @OptionalField(key: "sale_number")
+    var saleNumber: Int?
+
+    @Field(key: "created_at")
+    var createdAt: Date
+
+    // MARK: Initializers
+
+    init() {}
+
+    init(
+        conversationID: UUID,
+        senderID: UUID,
+        kind: Conversation.Entry.Kind,
+        body: String,
+        offerID: UUID? = nil,
+        saleNumber: Int? = nil,
+        at date: Date
+    ) {
+        self.$conversation.id = conversationID
+        self.$sender.id = senderID
+        self.kind = kind.rawValue
+        self.body = body
+        self.$offer.id = offerID
+        self.saleNumber = saleNumber
+        self.createdAt = date
+    }
+
+}