feat(web): include appearance in data bundles

[kilockok]

Split from #63.

内容：

• 桌面端“导出数据 / 导入数据”的 themes section 额外携带 themePreset、backgroundImage、backgroundImageOpacity
• 数据导入时恢复这些外观字段
• 数据导出/导入同步 sidebarGrouping
• 集中 GTD enabled storage 订阅逻辑，Sidebar 与 AppearanceSettings 复用同一入口

说明：

• 这不是独立的“主题导入/导出”入口；入口仍然是高级设置里的数据导入/导出。

验证：

• pnpm test -- src/tests/appearanceStorage.test.ts src/tests/advancedSettings.test.tsx
• pnpm type-check 受 main 既有 modelPicker.test.tsx is_default 类型错误阻塞

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[chatgpt-codex-connector]

Emit GTD change event even when storage write fails

When localStorage.setItem throws (e.g., quota exceeded or storage temporarily unavailable), writeGtdEnabled now swallows the error and skips dispatching arkloop:gtd-enabled-changed. In that case, components relying on subscribeGtdEnabled (like Sidebar) do not observe the toggle even though the settings UI already updated its local state, so grouping becomes inconsistent within the same tab. Previously this path still broadcasted the change from the click handler.

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[qqqqqf-q]

LGTM. normalizeThemeBackgroundImage 校验逻辑严谨，导入原子性正确（校验失败不写入部分状态）。subscribeGtdEnabled 集中化是合理改进。