feat: open Changes as a workspace tab (#2298)

Open the complete working comparison in a desktop workspace tab while preserving inline sidebar diffs when the tab is closed.

Working and commit comparisons share one diff panel, and workspace layout is the sole owner of live tab persistence and identity.

Refs #1520

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

@@ -768,6 +768,8 @@ export const en = {
         },
       },
       diff: {
+        openChangesTab: "Open Changes tab",
+        closeChangesTab: "Close Changes tab",
         binaryFile: "Binary file",
         tooLarge: "Diff too large to display",
         unified: "Unified diff",
@@ -1505,6 +1507,8 @@ export const en = {
       changesLabel: "Changes",
       changesSubtitle: "Working tree diff",
       commitSubtitle: "Commit diff",
+      uncommittedSubtitle: "Uncommitted changes",
+      baseSubtitle: "Compared with {{baseRef}}",
       directoryMissing: "Workspace directory not found.",
       empty: "No changes",
       loadError: "Failed to load diff",