feat: delete the selected note

Tests/ConjureKitTests/NotesStoreTests.swift

@@ -101,3 +101,33 @@ func noteTitlesUseFirstNonemptyLineAndCapAtSixtyCharacters() throws {
     try store.update(id: id, contents: NSAttributedString(string: " \t\n\n"))
     #expect(store.notes.first?.title == "Untitled Note")
 }
+
+@Test @MainActor
+func deletingNotesPersistsWithoutChangingOtherNotesAndPreservesMemoryOnFailure() throws {
+    let directory = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
+    let backup = directory.appendingPathExtension("backup")
+    defer {
+        try? FileManager.default.removeItem(at: directory)
+        try? FileManager.default.removeItem(at: backup)
+    }
+    let store = try NotesStore(directory: directory)
+    let deleted = try store.create()
+    let kept = try store.create()
+    try store.update(id: kept, contents: NSAttributedString(string: "Keep this note"))
+    try store.delete(id: deleted)
+    #expect(store.notes.map(\.id) == [kept])
+    #expect(try NotesStore(directory: directory).notes.map(\.id) == [kept])
+    #expect(throws: (any Error).self) { try store.delete(id: deleted) }
+
+    try FileManager.default.moveItem(at: directory, to: backup)
+    try Data("Blocked storage".utf8).write(to: directory)
+    #expect(throws: (any Error).self) { try store.delete(id: kept) }
+    #expect(store.notes.map(\.id) == [kept])
+    #expect(store.notes.first?.contents.string == "Keep this note")
+    try FileManager.default.removeItem(at: directory)
+    try FileManager.default.moveItem(at: backup, to: directory)
+    #expect(try NotesStore(directory: directory).notes.first?.contents.string == "Keep this note")
+    try store.delete(id: kept)
+    #expect(store.notes.isEmpty)
+    #expect(try NotesStore(directory: directory).notes.isEmpty)
+}