zeta: Improve reviewing UI (#21838)

Starting to fine-tune it.

| No edits scenario | Rated edits scenario |
|--------|--------|
| <img width="1577" alt="Screenshot 2024-12-11 at 01 57 46"
src="https://github.com/user-attachments/assets/42926e84-7a7f-4692-af44-672b52d3d377">
| <img width="1577" alt="Screenshot 2024-12-11 at 01 58 37"
src="https://github.com/user-attachments/assets/ee8ab0ef-75af-424c-b916-9f1ce8b5264d">

Release Notes:

- N/A

crates/ui/src/components/icon.rs

@@ -178,6 +178,7 @@ pub enum IconName {
     File,
     FileCode,
     FileDoc,
+    FileDiff,
     FileGeneric,
     FileGit,
     FileLock,
@@ -278,6 +279,8 @@ pub enum IconName {
     Tab,
     Terminal,
     TextSnippet,
+    ThumbsUp,
+    ThumbsDown,
     Trash,
     TrashAlt,
     Triangle,