docs: Update mentions to "assistant panel" (#53514)

We don't use this terminology anymore; now it's "agent panel".

Release Notes:

- N/A

docs/src/migrate/pycharm.md

@@ -119,7 +119,7 @@ If you chose the JetBrains keymap during onboarding, most of your shortcuts shou
 
 | Action            | Shortcut                   | Notes                          |
 | ----------------- | -------------------------- | ------------------------------ |
-| Toggle Right Dock | `Cmd + R`                  | Assistant panel, notifications |
+| Toggle Right Dock | `Cmd + R`                  | Agent panel, notifications     |
 | Split Panes       | `Cmd + K`, then arrow keys | Create splits in any direction |
 
 ### How to Customize Keybindings