🐛 fix(window): 修正启动窗口恢复到不可见区域

- 启动恢复普通窗口时先校验持久化 bounds 是否仍与可视区域相交
- 完全掉出可视区域时自动回正并回写新的窗口位置到 store
- 补充窗口恢复 helper 回归测试并验证前端构建通过

Fixes #384

frontend/src/utils/windowRestoreBounds.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from 'vitest';
+
+import { resolveVisibleStartupWindowBounds } from './windowRestoreBounds';
+
+describe('windowRestoreBounds', () => {
+  it('keeps existing bounds when the window still overlaps the visible area', () => {
+    expect(resolveVisibleStartupWindowBounds(
+      { width: 1280, height: 820, x: -120, y: 40 },
+      { availWidth: 1920, availHeight: 1080, availLeft: 0, availTop: 0 },
+    )).toEqual({ width: 1280, height: 820, x: -120, y: 40 });
+  });
+
+  it('recenters bounds when the saved window is fully outside the visible area', () => {
+    expect(resolveVisibleStartupWindowBounds(
+      { width: 1280, height: 820, x: 3200, y: 1800 },
+      { availWidth: 1920, availHeight: 1080, availLeft: 0, availTop: 0 },
+    )).toEqual({ width: 1280, height: 820, x: 320, y: 130 });
+  });
+
+  it('recenters bounds when the saved window is fully above and left of the visible area', () => {
+    expect(resolveVisibleStartupWindowBounds(
+      { width: 900, height: 640, x: -1600, y: -900 },
+      { availWidth: 1600, availHeight: 900, availLeft: 0, availTop: 0 },
+    )).toEqual({ width: 900, height: 640, x: 350, y: 130 });
+  });
+});