feat(workspace): add no-folder empty states and gate folder-only actions

- Sidebar: replace the "no conversations" placeholder with Open Folder, Clone Repository, and Project Boot buttons when the workspace has no open folders.
- Title bar: disable the terminal and auxiliary-panel toggle buttons while no folder is active.
- Aux panel: show a shared localized "no folder open" prompt in the file tree, git changes, and git log tabs when no folder is active.
- Add auxPanel.noFolderTitle / noFolderHint translations across all ten supported locales.

src/components/layout/aux-panel-file-tree-tab.tsx

@@ -19,6 +19,7 @@ import { useTabContext } from "@/contexts/tab-context"
 import { useTerminalContext } from "@/contexts/terminal-context"
 import { useWorkspaceContext } from "@/contexts/workspace-context"
 import { useWorkspaceStateStore } from "@/hooks/use-workspace-state-store"
+import { AuxPanelNoFolderEmpty } from "@/components/layout/aux-panel-no-folder-empty"
 import { WorkspaceDegradedBanner } from "@/components/layout/workspace-degraded-banner"
 import {
   createFileTreeEntry,
@@ -2098,6 +2099,10 @@ export function FileTreeTab() {
     workspaceState.seq,
   ])
 
+  if (!folder) {
+    return <AuxPanelNoFolderEmpty />
+  }
+
   if (loading && nodes.length === 0) {
     return (
       <div className="p-3 space-y-2">