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/i18n/resources/en.ts

@@ -585,6 +585,7 @@ export const en = {
         renameAgent: "Rename agent",
       },
       actions: {
+        newTab: "New tab",
         newAgent: "New agent",
         newTerminal: "New terminal",
         preparingTerminal: "Preparing terminal tab",
@@ -593,6 +594,9 @@ export const en = {
         exitFocusMode: "Exit focus mode",
         splitRight: "Split pane right",
         splitDown: "Split pane down",
+        changes: "Changes",
+        files: "Files",
+        pullRequest: "Pull request",
         terminalProfilesMenu: "Terminal profiles",
         editTerminalProfiles: "Edit profiles…",
         pinTarget: "Pin",
@@ -1668,6 +1672,17 @@ export const en = {
         reloadMessage: "Your local changes will be lost.",
       },
     },
+    files: {
+      label: "Files",
+      subtitle: "Workspace files",
+      tooltip: "Browse workspace files",
+    },
+    pullRequest: {
+      label: "Pull request",
+      subtitle: "Pull request details",
+      emptyTitle: "No pull request yet",
+      emptyDescription: "Create a pull request for this checkout to see its details here.",
+    },
     diff: {
       changesLabel: "Changes",
       changesSubtitle: "Working tree diff",