Add optional sync between Macs with a shared 8-digit code

Notes and photos were stuck on one machine. A small Go/Postgres backend
stores each group's payload under a code that doubles as the shared
secret, so a second Mac just needs the code — no account or login.

Applying a remote change must not push it straight back, otherwise the
two Macs would bump the version back and forth forever, so payloads are
fingerprinted and identical ones are skipped.

💘 Generated with Crush

Assisted-by: Crush:kimi-k3

Sources/Prompt/Store.swift

@@ -47,7 +47,7 @@ final class Store: ObservableObject {
         try? FileManager.default.createDirectory(at: imagesDirectory, withIntermediateDirectories: true)
         load()
         if sections.isEmpty {
-            let workspace = Section(name: "Workspace")
+            let workspace = Section(name: "Default")
             sections = [workspace]
             activeSectionID = workspace.id
             save()
@@ -77,6 +77,41 @@ final class Store: ObservableObject {
         let file = StoreFile(sections: sections, activeSectionID: activeSectionID)
         guard let data = try? JSONEncoder().encode(file) else { return }
         try? data.write(to: storeFile, options: .atomic)
+        onDidChange?()
+    }
+
+    // MARK: - Sync support
+
+    /// Called after every save so `SyncService` can push the change.
+    var onDidChange: (() -> Void)?
+
+    func replaceAll(sections newSections: [Section], activeSectionID newActiveSectionID: UUID?) {
+        sections = newSections
+        if let newActiveSectionID, newSections.contains(where: { $0.id == newActiveSectionID }) {
+            activeSectionID = newActiveSectionID
+        } else {
+            activeSectionID = newSections.first?.id
+        }
+        save()
+    }
+
+    func imageData(for filename: String) -> Data? {
+        try? Data(contentsOf: imagesDirectory.appendingPathComponent(filename))
+    }
+
+    func importImage(filename: String, data: Data) {
+        let url = imagesDirectory.appendingPathComponent(filename)
+        if let existing = try? Data(contentsOf: url), existing == data { return }
+        try? data.write(to: url)
+        imageCache.removeObject(forKey: filename as NSString)
+    }
+
+    func cleanupOrphanedImages(referenced: Set<String>) {
+        let files = (try? FileManager.default.contentsOfDirectory(at: imagesDirectory, includingPropertiesForKeys: nil)) ?? []
+        for file in files where !referenced.contains(file.lastPathComponent) {
+            try? FileManager.default.removeItem(at: file)
+            imageCache.removeObject(forKey: file.lastPathComponent as NSString)
+        }
     }
 
     // MARK: - Sections