assistant2: Add design refinements (#27160)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Agus Zubiaga <hi@aguz.me>

crates/ui/src/components/icon.rs

@@ -143,6 +143,7 @@ pub enum IconName {
     ArrowUp,
     ArrowUpFromLine,
     ArrowUpRight,
+    ArrowUpRightAlt,
     AtSign,
     AudioOff,
     AudioOn,
@@ -156,6 +157,7 @@ pub enum IconName {
     Book,
     BookCopy,
     BookPlus,
+    Brain,
     CaseSensitive,
     Check,
     ChevronDown,