Fix SF Symbol and add tests for addAttachedFile

- Use doc.on.clipboard instead of clipboard for the Paste menu item,
  which is the standard iOS paste icon (available since iOS 13)
- Add ChatViewModelTests for addAttachedFile: verifies lastPathComponent
  extraction and that multiple calls each append correctly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: mcintyre94

Wisp/Views/SpriteDetail/Chat/ChatAttachmentButton.swift

@@ -36,7 +36,7 @@ struct ChatAttachmentButton: View {
                     Button {
                         onPasteFromClipboard()
                     } label: {
-                        Label("Paste from Clipboard", systemImage: "clipboard")
+                        Label("Paste from Clipboard", systemImage: "doc.on.clipboard")
                     }
                 }
             } label: {

WispTests/ChatViewModelTests.swift

@@ -829,6 +829,31 @@ struct ChatViewModelTests {
         }
     }
 
+    // MARK: - addAttachedFile
+
+    @Test func addAttachedFile_appendsWithLastPathComponent() throws {
+        let ctx = try makeModelContext()
+        let (vm, _) = makeChatViewModel(modelContext: ctx)
+
+        vm.addAttachedFile(remotePath: "/home/sprite/project/photo_20260312_120000.png")
+
+        #expect(vm.attachedFiles.count == 1)
+        #expect(vm.attachedFiles[0].name == "photo_20260312_120000.png")
+        #expect(vm.attachedFiles[0].path == "/home/sprite/project/photo_20260312_120000.png")
+    }
+
+    @Test func addAttachedFile_appendsMultiple() throws {
+        let ctx = try makeModelContext()
+        let (vm, _) = makeChatViewModel(modelContext: ctx)
+
+        vm.addAttachedFile(remotePath: "/home/sprite/project/file1.txt")
+        vm.addAttachedFile(remotePath: "/home/sprite/project/file2.py")
+
+        #expect(vm.attachedFiles.count == 2)
+        #expect(vm.attachedFiles[0].name == "file1.txt")
+        #expect(vm.attachedFiles[1].name == "file2.py")
+    }
+
     @Test func stashDraft_leavesInputReadyForNextMessage() throws {
         let ctx = try makeModelContext()
         let (vm, _) = makeChatViewModel(modelContext: ctx)