Expand workspace panel actions and keyboard navigation (#3685)

* fix(app): keep file navigation in place

Retargeting a File tab allocated a new tab identity, causing the tab track to unmount and remount during navigation. Preserve the identity for File-to-File changes while retaining new instances for cross-kind replacements.

* feat(app): expand workspace panel actions

Keep the Command Center aligned with workspace tab and pane primitives. Add explicit panel placement, focused open behavior, keyboard navigation for empty panes, and a Changes pill that toggles the visible Side panel without closing its tab.

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

@@ -61,6 +61,9 @@ export const en = {
       workspaces: "Workspaces",
       agents: "Agents",
       newAgent: "New agent",
+      open: "Open {{name}}",
+      openInSidePanel: "Open {{name}} in Side panel",
+      openInFocusedPane: "Open {{name}} in focused pane",
       addProject: "Add project",
       home: "Home",
       groupByProject: "Group by project",