assistant2: Add tiny design improvements (#27399)

Really small stuff, like adding icons and adjusting colors.

Release Notes:

- N/A

assets/icons/arrow_right_left.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-arrow-right-left"><path d="m16 3 4 4-4 4"/><path d="M20 7H4"/><path d="m8 21-4-4 4-4"/><path d="M4 17h16"/></svg>

assets/icons/cog.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-cog"><path d="M12 20a8 8 0 1 0 0-16 8 8 0 0 0 0 16Z"/><path d="M12 14a2 2 0 1 0 0-4 2 2 0 0 0 0 4Z"/><path d="M12 2v2"/><path d="M12 22v-2"/><path d="m17 20.66-1-1.73"/><path d="M11 10.27 7 3.34"/><path d="m20.66 17-1.73-1"/><path d="m3.34 7 1.73 1"/><path d="M14 12h8"/><path d="M2 12h2"/><path d="m20.66 7-1.73 1"/><path d="m3.34 17 1.73-1"/><path d="m17 3.34-1 1.73"/><path d="m11 13.73-4 6.93"/></svg>