✨ feat(ai-entry): 优化AI助手贴边入口交互体验

- 将 AI 助手入口从侧栏工具区迁移为主内容区右侧贴边标签
- 调整打开态贴边标签锚点到面板左外沿，避免遮挡头部操作区
- 重排侧栏顶部工具布局，恢复四项按钮的稳定网格结构
- 新增 aiEntryLayout 布局辅助与回归测试，覆盖打开态附着位置

frontend/src/utils/aiEntryLayout.test.ts

@@ -0,0 +1,71 @@
+import { describe, expect, it } from 'vitest';
+import {
+  SIDEBAR_UTILITY_ITEM_KEYS,
+  resolveAIEntryPlacement,
+  resolveAIEdgeHandleAttachment,
+  resolveAIEdgeHandleDockStyle,
+  resolveAIEdgeHandleStyle,
+} from './aiEntryLayout';
+
+describe('ai entry layout', () => {
+  it('keeps the sidebar utility group free of the AI entry', () => {
+    expect(SIDEBAR_UTILITY_ITEM_KEYS).toEqual(['tools', 'proxy', 'theme', 'about']);
+  });
+
+  it('anchors the AI entry to the content edge', () => {
+    expect(resolveAIEntryPlacement()).toBe('content-edge');
+  });
+
+  it('attaches the closed handle to the content shell', () => {
+    expect(resolveAIEdgeHandleAttachment(false)).toBe('content-shell');
+  });
+
+  it('attaches the open handle to the panel shell', () => {
+    expect(resolveAIEdgeHandleAttachment(true)).toBe('panel-shell');
+  });
+
+  it('keeps the closed handle docked on the content edge', () => {
+    expect(resolveAIEdgeHandleDockStyle('content-shell')).toMatchObject({
+      position: 'absolute',
+      top: 16,
+      right: 0,
+      zIndex: 12,
+    });
+  });
+
+  it('keeps the open handle outside the panel shell to avoid header overlap', () => {
+    expect(resolveAIEdgeHandleDockStyle('panel-shell')).toMatchObject({
+      position: 'absolute',
+      top: 16,
+      right: '100%',
+      zIndex: 12,
+    });
+  });
+
+  it('uses the attached active appearance when the AI panel is open', () => {
+    const style = resolveAIEdgeHandleStyle({
+      darkMode: true,
+      aiPanelVisible: true,
+      effectiveUiScale: 1,
+    });
+
+    expect(style.color).toBe('#ffd666');
+    expect(style.background).toBe('rgba(255,214,102,0.12)');
+    expect(style.borderRadius).toBe('10px 0 0 10px');
+    expect(style.borderRight).toBe('none');
+    expect(style.height).toBe(24);
+  });
+
+  it('uses the subdued attached appearance when the AI panel is closed', () => {
+    const style = resolveAIEdgeHandleStyle({
+      darkMode: false,
+      aiPanelVisible: false,
+      effectiveUiScale: 1,
+    });
+
+    expect(style.color).toBe('rgba(22,32,51,0.82)');
+    expect(style.background).toBe('rgba(15,23,42,0.04)');
+    expect(style.paddingInline).toBe(8);
+    expect(style.borderRadius).toBe('10px 0 0 10px');
+  });
+});