docs: Update agent settings content (#39303)

Removes the preview note of the `buffer_font_size` used for agent panel
buffers, now that's available in stable as of 206.6. Also ended up
removing the "available in agent settings UI" thing because... that will
very soon not be needed to be called out.

Release Notes:

- N/A

docs/src/ai/agent-settings.md

@@ -134,7 +134,7 @@ Use the `agent_font_size` setting to change the font size of rendered agent resp
 }
 ```
 
-> (Preview Version Note): Editors in the Agent Panel—whether that is the main message textarea or previous messages—use monospace fonts and therefore, are controlled by the `buffer_font_size` setting, which is defined globally in your `settings.json`.
+> Editors in the Agent Panel—whether that is the main message textarea or previous messages—use monospace fonts and therefore, are controlled by the `buffer_font_size` setting, which is defined globally in your `settings.json`.
 
 ### Auto-run Commands
 
@@ -149,8 +149,6 @@ The default value is `false`.
 }
 ```
 
-> This setting is available via the Agent Panel's settings UI.
-
 ### Single-file Review
 
 Control whether you want to see review actions (accept & reject) in single buffers after the agent is done performing edits.
@@ -166,8 +164,6 @@ The default value is `false`.
 
 When set to false, these controls are only available in the multibuffer review tab.
 
-> This setting is available via the Agent Panel's settings UI.
-
 ### Sound Notification
 
 Control whether you want to hear a notification sound when the agent is done generating changes or needs your input.
@@ -181,8 +177,6 @@ The default value is `false`.
 }
 ```
 
-> This setting is available via the Agent Panel's settings UI.
-
 ### Message Editor Size
 
 Use the `message_editor_min_lines` setting to control minimum number of lines of height the agent message editor should have.
@@ -210,8 +204,6 @@ The default value is `false`.
 }
 ```
 
-> This setting is available via the Agent Panel's settings UI.
-
 ### Edit Card
 
 Use the `expand_edit_card` setting to control whether edit cards show the full diff in the Agent Panel.