v1.2.1: UX fixes for tool display, shell access, and session restore

- Show "File changes" label on collapsed code diff views when no title
- Reinforce shell command availability in agent system prompt
- Persist working directory for agent/viewer panes on session save
- Remove unused make_nsstring import

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/ai/blocklist/inline_action/code_diff_view.rs

@@ -1536,9 +1536,10 @@ impl CodeDiffView {
             .with_main_axis_alignment(MainAxisAlignment::Start)
             .with_cross_axis_alignment(CrossAxisAlignment::Center);
 
-        if let Some(title) = &self.title {
+        {
+            let title_text = self.title.as_deref().unwrap_or("File changes");
             let title = Text::new_inline(
-                title.to_string(),
+                title_text.to_string(),
                 appearance.ui_font_family(),
                 appearance.monospace_font_size(),
             )
@@ -1763,9 +1764,10 @@ impl CodeDiffView {
         }
 
         let mut col = Flex::column();
-        if let Some(title) = &self.title {
+        {
+            let title_text = self.title.as_deref().unwrap_or("File changes");
             let title = Text::new_inline(
-                title.to_string(),
+                title_text.to_string(),
                 appearance.ui_font_family(),
                 appearance.monospace_font_size() + 2.,
             )