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/panels/register-panels.ts

@@ -3,10 +3,12 @@ import { browserPanelRegistration } from "@/desktop/browser/panel";
 import { commitDiffPanelRegistration, workingDiffPanelRegistration } from "@/panels/diff-panel";
 import { draftPanelRegistration } from "@/panels/draft-panel";
 import { filePanelRegistration } from "@/panels/file-panel";
+import { filesPanelRegistration } from "@/panels/files-panel";
 import { registerPanel } from "@/panels/panel-registry";
 import { setupPanelRegistration } from "@/panels/setup-panel";
 import { terminalPanelRegistration } from "@/panels/terminal-panel";
 import { providerSubagentPanelRegistration } from "@/panels/provider-subagent-panel";
+import { pullRequestPanelRegistration } from "@/panels/pull-request-panel";
 
 let panelsRegistered = false;
 
@@ -21,6 +23,8 @@ export function ensurePanelsRegistered(): void {
   registerPanel(terminalPanelRegistration);
   registerPanel(browserPanelRegistration);
   registerPanel(filePanelRegistration);
+  registerPanel(filesPanelRegistration);
+  registerPanel(pullRequestPanelRegistration);
   registerPanel(commitDiffPanelRegistration);
   registerPanel(workingDiffPanelRegistration);
   panelsRegistered = true;