fix(library): prevent right-click from deleting book group on Windows

[linze0721]

Summary

Fix right-click on book groups immediately deleting them on Windows instead of showing a context menu.

Closes #465

Root Cause

The group card and sidebar group components treated right-click the same as a regular click/long-press, which triggered the delete flow directly. The delete confirmation dialog appeared after the group was already removed.

Changes

• packages/app/src/components/home/GroupCard.tsx: Added an onContextMenu handler that opens a Rename/Delete context menu on right-click, preventing the default behavior and the immediate delete path.
• packages/app/src/components/home/HomePage.tsx: Added delete confirmation (window.confirm) before calling removeGroup().
• packages/app/src/components/layout/Sidebar.tsx: Reworked sidebar group right-click to show a proper context menu with Rename and Delete options, with delete confirmation before removal.

Verification

• pnpm install --frozen-lockfile ✅
• npm run build ✅

[codedogQBY]

中文：
验证 #487 时发现删除确认仍然有问题，需要修改后再合并。

失败场景：

1. 首页分组卡片：右键打开菜单后点击“删除”，分组会在未点击确认的情况下被删除。预期：必须先弹出确认，并且只有用户明确确认后才调用 removeGroup；取消或未确认时不能删除。
2. 左侧栏分组 chip：右键打开菜单后点击“删除”，同样会在未点击确认的情况下删除。预期同上。

建议不要依赖当前的删除入口直接继续执行删除逻辑，可以改成项目内已有的确认弹窗/对话框，或确保 removeGroup 只会在确认回调返回 true 后执行。请同时覆盖 GroupCard 和 Sidebar 两个入口。

English:
I tested #487 and the delete confirmation flow is still broken, so this should be fixed before merging.

Failing cases:

1. Home group card: after opening the context menu and clicking Delete, the group is deleted without an explicit confirmation click. Expected: show a confirmation first, and call removeGroup only after the user explicitly confirms. Cancel/no confirmation must not delete the group.
2. Sidebar group chip: right-click menu Delete has the same issue. Expected behavior is the same.

Please avoid letting the delete action fall through immediately. Prefer the app's existing confirmation dialog/modal, or otherwise ensure removeGroup is invoked only after the confirmation result is true. Please fix both GroupCard and Sidebar paths.