agent: Add design adjustments to message editor (#29891)

- Removed unused `MessageBubbleDashed` icon
- Polished `Crosshair` icon SVG
- Added dropdown toggle keybinding to the profile selector tooltip
- Repositioned buttons at the message editor footer
- Updated buttons to use `Button` instead of `ButtonLike`

Release Notes:

- N/A

crates/icons/src/icons.rs

@@ -160,7 +160,6 @@ pub enum IconName {
     Maximize,
     Menu,
     MenuAlt,
-    MessageBubbleDashed,
     MessageBubbles,
     Mic,
     MicMute,