feat(import): say which fields differ, and stop offering to apply nothing

A row marked "edited" or "conflict" gave no way to tell what actually
differs, so a resource that drifted from the file — however it drifted —
reads as an unexplained accusation. The plan now carries the field names
the source and the local copy disagree on, and the row's tooltip lists
them.

The preview's primary button also read "Apply" when the current selection
would change nothing. It now reads "Done", since committing an empty
selection only records the decisions made in the preview.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/yaak-client/components/ImportDataDialog.tsx

@@ -345,6 +345,7 @@ function LoadedImportDataDialog({
           modelId: existing?.id ?? planned?.id ?? "workspace",
           name: existing?.name ?? planned?.name ?? "New workspace",
           selected: true,
+          changedFields: [],
         },
         children: itemTree,
       };
@@ -408,7 +409,7 @@ function LoadedImportDataDialog({
               ? "Importing"
               : changeCount > 0
                 ? `Apply ${changeCount} ${changeCount === 1 ? "Change" : "Changes"}`
-                : "Apply"}
+                : "Done"}
           </Button>
         </HStack>
       </VStack>
@@ -626,19 +627,23 @@ function actionLabel(item: ImportPlanItem): string | null {
 }
 
 function actionHelp(item: ImportPlanItem): string | null {
+  const help = (text: string) =>
+    item.changedFields.length > 0
+      ? `${text} · ${item.changedFields.map(fieldLabel).join(", ")}`
+      : text;
   switch (item.action) {
     case "create":
       return "Added since the last import";
     case "update":
-      return "Changed since the last import";
+      return help("Changed since the last import");
     case "delete":
       return item.reason === "moved_into_not_imported_folder"
         ? "Moved into a folder that isn't imported. Import that folder instead to follow the move"
         : "Deleted since the last import";
     case "keep_local":
-      return "Local edits made since the last import. Importing will revert them if checked";
+      return help("Local edits made since the last import. Importing will revert them if checked");
     case "conflict":
-      return "Changed both here and in the file since the last import";
+      return help("Changed both here and in the file since the last import");
     case "not_imported":
       return "In the file, but not imported. Check it to import it";
     default:
@@ -646,6 +651,10 @@ function actionHelp(item: ImportPlanItem): string | null {
   }
 }
 
+function fieldLabel(field: string): string {
+  return field.replace(/([A-Z])/g, " $1").toLowerCase();
+}
+
 /** Every plan item above `item`, nearest first. */
 function ancestorsOf(item: ImportPlanItem, byId: Map<string, ImportPlanItem>): ImportPlanItem[] {
   const ancestors: ImportPlanItem[] = [];