assistant2: Adjust spacing and icons on the context picker (#23607)

Just fine-tuning spacing, icon size and color, and ensure they're are
consistent throughout.

Release Notes:

- N/A

crates/assistant2/src/context_picker/directory_context_picker.rs

@@ -234,7 +234,12 @@ impl PickerDelegate for DirectoryContextPickerDelegate {
             ListItem::new(ix)
                 .inset(true)
                 .toggle_state(selected)
-                .child(h_flex().gap_2().child(Label::new(directory_name)))
+                .start_slot(
+                    Icon::new(IconName::Folder)
+                        .size(IconSize::XSmall)
+                        .color(Color::Muted),
+                )
+                .child(Label::new(directory_name))
                 .when(added, |el| {
                     el.end_slot(
                         h_flex()

crates/assistant2/src/context_picker/file_context_picker.rs

@@ -396,12 +396,12 @@ pub fn render_file_context_entry(
 
     h_flex()
         .id(id)
-        .gap_1()
+        .gap_1p5()
         .w_full()
-        .child(file_icon.size(IconSize::Small))
+        .child(file_icon.size(IconSize::Small).color(Color::Muted))
         .child(
             h_flex()
-                .gap_2()
+                .gap_1()
                 .child(Label::new(file_name))
                 .children(directory.map(|directory| {
                     Label::new(directory)
@@ -409,11 +409,12 @@ pub fn render_file_context_entry(
                         .color(Color::Muted)
                 })),
         )
-        .child(div().w_full())
         .when_some(added, |el, added| match added {
             FileInclusion::Direct(_) => el.child(
                 h_flex()
-                    .gap_1()
+                    .w_full()
+                    .justify_end()
+                    .gap_0p5()
                     .child(
                         Icon::new(IconName::Check)
                             .size(IconSize::Small)
@@ -426,7 +427,9 @@ pub fn render_file_context_entry(
 
                 el.child(
                     h_flex()
-                        .gap_1()
+                        .w_full()
+                        .justify_end()
+                        .gap_0p5()
                         .child(
                             Icon::new(IconName::Check)
                                 .size(IconSize::Small)

crates/assistant2/src/context_picker/thread_context_picker.rs

@@ -209,9 +209,13 @@ pub fn render_thread_context_entry(
     });
 
     h_flex()
-        .gap_1()
+        .gap_1p5()
         .w_full()
-        .child(Icon::new(IconName::MessageCircle).size(IconSize::Small))
+        .child(
+            Icon::new(IconName::MessageCircle)
+                .size(IconSize::XSmall)
+                .color(Color::Muted),
+        )
         .child(Label::new(thread.summary.clone()))
         .child(div().w_full())
         .when(added, |el| {