Restore compact Changes diff controls (#1945)

* feat(app): restore compact Changes diff controls

Keep the folder tree behind a view toggle while preserving the flat file list as the default.

Move secondary diff options into the overflow menu so the Changes toolbar stays compact.

* fix(app): mirror whitespace diff option copy

* fix(app): polish diff controls review follow-up

packages/app/src/i18n/resources/en.ts

@@ -714,7 +714,13 @@ export const en = {
         tooLarge: "Diff too large to display",
         unified: "Unified diff",
         split: "Side-by-side diff",
+        switchToUnified: "Switch to unified diff",
+        switchToSplit: "Switch to side-by-side diff",
+        showTreeView: "Show folder tree",
+        showFlatView: "Show flat file list",
+        options: "Diff options",
         hideWhitespace: "Hide whitespace",
+        showWhitespace: "Show whitespace",
         scrollLongLines: "Scroll long lines",
         wrapLongLines: "Wrap long lines",
         collapseAll: "Collapse all files",