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

assets/icons/file_diff.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-file-diff"><path d="M15 2H6a2 2 0 0 0-2 2v16a2 2 0 0 0 2 2h12a2 2 0 0 0 2-2V7Z"/><path d="M9 10h6"/><path d="M12 13V7"/><path d="M9 17h6"/></svg>

assets/icons/thumbs_down.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-thumbs-down"><path d="M17 14V2"/><path d="M9 18.12 10 14H4.17a2 2 0 0 1-1.92-2.56l2.33-8A2 2 0 0 1 6.5 2H20a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2h-2.76a2 2 0 0 0-1.79 1.11L12 22a3.13 3.13 0 0 1-3-3.88Z"/></svg>

assets/icons/thumbs_up.svg

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+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-thumbs-up"><path d="M7 10v12"/><path d="M15 5.88 14 10h5.83a2 2 0 0 1 1.92 2.56l-2.33 8A2 2 0 0 1 17.5 22H4a2 2 0 0 1-2-2v-8a2 2 0 0 1 2-2h2.76a2 2 0 0 0 1.79-1.11L12 2a3.13 3.13 0 0 1 3 3.88Z"/></svg>