Make the workspace right pane a first-class tab host (#3287)

* feat(app): add persistent workspace side panes

Keep the common review and file-browsing workflow beside the active agent without tearing down pane contents. Workspace tabs now share one compact chip language, assistant file links route into the retained right pane, and diff/file trees share stable geometry.

* fix(app): localize pull request empty state

* test(app): update explorer pane coverage

* fix(app): preserve explorer pane workflows

* test(app): make explorer tab selection idempotent

* fix(app): persist workspace review pins

* fix(app): preserve sidebar scrim drag hook

* fix(app): restore companion pane interactions

* test(app): follow selected sidebar surface

packages/app/src/assistant-file-links/use-file-link.test.tsx

@@ -136,7 +136,6 @@ describe("useFileLink", () => {
     expect(result.current).toBe(first);
     expect(result.current.onHoverIn).toBe(first.onHoverIn);
     expect(result.current.onPress).toBe(first.onPress);
-    expect(result.current.onAuxPress).toBe(first.onAuxPress);
     expect(result.current.open).toBe(first.open);
   });
 
@@ -177,7 +176,7 @@ describe("useFileLink", () => {
             lineStart: undefined,
             lineEnd: undefined,
           },
-          disposition: "main",
+          disposition: "side",
         },
       ]);
     });