Refactor: Improve UI rendering and address code review comments

This commit addresses several code review comments primarily focused on improving the rendering and stability of the CLI UI.

Key changes include:
- Passing `isPending` and `availableTerminalHeight` props to `MarkdownDisplay` to enable more intelligent rendering of content, especially for pending messages and code blocks.
- Adjusting height calculations in `ToolGroupMessage` and `ToolMessage` to more accurately reflect available space.
- Refining the logic in `App.tsx` for measuring and utilizing terminal height, including renaming `footerRef` to `mainControlsRef` for clarity.
- Ensuring consistent prop drilling for `isPending` and `availableTerminalHeight` through `HistoryItemDisplay`, `GeminiMessage`, and `GeminiMessageContent`.
- In `MarkdownDisplay`, when `isPending` is true and content exceeds `availableTerminalHeight`, the code block will now be truncated with a "... generating more ..." message. If there's insufficient space even for the
message, a simpler "... code is being written ..." will be shown.

packages/cli/src/ui/components/messages/ToolGroupMessage.tsx

@@ -29,7 +29,6 @@ export const ToolGroupMessage: React.FC<ToolGroupMessageProps> = ({
   const borderColor = hasPending ? Colors.AccentYellow : Colors.SubtleComment;
 
   const staticHeight = /* border */ 2 + /* marginBottom */ 1;
-  availableTerminalHeight -= staticHeight;
 
   return (
     <Box
@@ -58,7 +57,7 @@ export const ToolGroupMessage: React.FC<ToolGroupMessageProps> = ({
             resultDisplay={tool.resultDisplay}
             status={tool.status}
             confirmationDetails={tool.confirmationDetails}
-            availableTerminalHeight={availableTerminalHeight}
+            availableTerminalHeight={availableTerminalHeight - staticHeight}
           />
           {tool.status === ToolCallStatus.Confirming &&
             tool.confirmationDetails && (