🐛 fix(sidebar): 放宽左侧树拖拽宽度上限

- 统一侧栏宽度常量，最大宽度放宽到 960px
- 拖拽时按窗口宽度预留主工作区空间
- 同步 v2 与 legacy 侧栏 CSS 最大宽度
- 持久化侧栏宽度时允许保存更宽配置并补充测试

frontend/src/utils/sidebarLayout.test.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest';
+import {
+  DEFAULT_SIDEBAR_WIDTH,
+  SIDEBAR_RESIZE_MAX_WIDTH,
+  SIDEBAR_RESIZE_MIN_WIDTH,
+  resolveSidebarResizeMaxWidth,
+  sanitizeSidebarWidth,
+} from './sidebarLayout';
+
+describe('sidebar layout bounds', () => {
+  it('allows wider persisted sidebar widths while keeping invalid values safe', () => {
+    expect(sanitizeSidebarWidth(880)).toBe(880);
+    expect(sanitizeSidebarWidth(1200)).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+    expect(sanitizeSidebarWidth(120)).toBe(SIDEBAR_RESIZE_MIN_WIDTH);
+    expect(sanitizeSidebarWidth('bad')).toBe(DEFAULT_SIDEBAR_WIDTH);
+  });
+
+  it('keeps enough workbench space when resolving drag width on smaller windows', () => {
+    expect(resolveSidebarResizeMaxWidth(1600)).toBe(SIDEBAR_RESIZE_MAX_WIDTH);
+    expect(resolveSidebarResizeMaxWidth(1180)).toBe(820);
+    expect(resolveSidebarResizeMaxWidth(480)).toBe(SIDEBAR_RESIZE_MIN_WIDTH);
+  });
+});

frontend/src/utils/sidebarLayout.ts

@@ -0,0 +1,27 @@
+export const DEFAULT_SIDEBAR_WIDTH = 330;
+export const SIDEBAR_RESIZE_MIN_WIDTH = 200;
+export const SIDEBAR_SIDER_MIN_WIDTH = 232;
+export const SIDEBAR_RESIZE_MAX_WIDTH = 960;
+export const SIDEBAR_MIN_WORKBENCH_WIDTH = 360;
+
+export const resolveSidebarResizeMaxWidth = (
+  viewportWidth: unknown,
+  minWidth = SIDEBAR_RESIZE_MIN_WIDTH,
+): number => {
+  const parsedViewportWidth = Number(viewportWidth);
+  if (!Number.isFinite(parsedViewportWidth) || parsedViewportWidth <= 0) {
+    return SIDEBAR_RESIZE_MAX_WIDTH;
+  }
+
+  const viewportLimitedWidth = Math.trunc(parsedViewportWidth) - SIDEBAR_MIN_WORKBENCH_WIDTH;
+  return Math.max(minWidth, Math.min(SIDEBAR_RESIZE_MAX_WIDTH, viewportLimitedWidth));
+};
+
+export const sanitizeSidebarWidth = (value: unknown): number => {
+  const parsed = Number(value);
+  if (!Number.isFinite(parsed)) return DEFAULT_SIDEBAR_WIDTH;
+  return Math.max(
+    SIDEBAR_RESIZE_MIN_WIDTH,
+    Math.min(SIDEBAR_RESIZE_MAX_WIDTH, Math.trunc(parsed)),
+  );
+};