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/GeminiMessageContent.tsx

@@ -10,6 +10,8 @@ import { MarkdownDisplay } from '../../utils/MarkdownDisplay.js';
 
 interface GeminiMessageContentProps {
   text: string;
+  isPending: boolean;
+  availableTerminalHeight: number;
 }
 
 /*
@@ -20,13 +22,19 @@ interface GeminiMessageContentProps {
  */
 export const GeminiMessageContent: React.FC<GeminiMessageContentProps> = ({
   text,
+  isPending,
+  availableTerminalHeight,
 }) => {
   const originalPrefix = '✦ ';
   const prefixWidth = originalPrefix.length;
 
   return (
     <Box flexDirection="column" paddingLeft={prefixWidth}>
-      <MarkdownDisplay text={text} />
+      <MarkdownDisplay
+        text={text}
+        isPending={isPending}
+        availableTerminalHeight={availableTerminalHeight}
+      />
     </Box>
   );
 };