feat(cli): add agent composer UI and refactor text input handling

- Extract shared BaseTextInput component with readline keyboard handling
- Add AgentComposer and AgentFooter components for agent interaction
- Add useAgentStreamingState hook for managing agent streaming state
- Refactor InputPrompt to use BaseTextInput with agent tab bar focus support
- Move calculatePromptWidths to shared layoutUtils
- Disable auto-accept indicator on agent tabs (agents handle their own)

This enables a dedicated input experience for agent tabs with proper
focus management and keyboard navigation between main input and agent tabs.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/cli/src/ui/utils/layoutUtils.ts

@@ -0,0 +1,40 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Shared layout calculation utilities for the terminal UI.
+ */
+
+/**
+ * Calculate the widths for the input prompt area based on terminal width.
+ *
+ * Returns the content width (for the text buffer), the total container width
+ * (including border + padding + prefix), the suggestions dropdown width,
+ * and the frame overhead constant.
+ */
+export const calculatePromptWidths = (terminalWidth: number) => {
+  const widthFraction = 0.9;
+  const FRAME_PADDING_AND_BORDER = 4; // Border (2) + padding (2)
+  const PROMPT_PREFIX_WIDTH = 2; // '> ' or '! '
+  const MIN_CONTENT_WIDTH = 2;
+
+  const innerContentWidth =
+    Math.floor(terminalWidth * widthFraction) -
+    FRAME_PADDING_AND_BORDER -
+    PROMPT_PREFIX_WIDTH;
+
+  const inputWidth = Math.max(MIN_CONTENT_WIDTH, innerContentWidth);
+  const FRAME_OVERHEAD = FRAME_PADDING_AND_BORDER + PROMPT_PREFIX_WIDTH;
+  const containerWidth = inputWidth + FRAME_OVERHEAD;
+  const suggestionsWidth = Math.max(20, Math.floor(terminalWidth * 1.0));
+
+  return {
+    inputWidth,
+    containerWidth,
+    suggestionsWidth,
+    frameOverhead: FRAME_OVERHEAD,
+  } as const;
+};