feat(calendar): simplify holiday highlight styles and improve accessibility

- Introduced a new visual style for holiday highlights in the calendar component, replacing complex gradients with solid colors for better clarity.
- Removed the holiday badge to reduce visual noise and enhance user experience.
- Ensured that holiday information remains accessible through long-press interactions.
- Updated specifications to reflect the new design decisions and requirements for both light and dark themes.
- Added tasks for implementation, including style adjustments and accessibility enhancements.

openspec/changes/archive/2026-02-12-simplify-calendar-holiday-highlight/proposal.md

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+## Why
+
+当前日历节假日的视觉呈现过于复杂，多种状态叠加（节假日、工作日、选中、有数据等）导致视觉混乱。渐变背景和红色徽章增加了视觉噪音，影响用户快速浏览日历的体验。需要简化节假日高亮样式，提升界面清晰度和可维护性。
+
+## What Changes
+
+- **移除复杂的渐变背景**：将节假日的绿色/橙色渐变背景改为简洁的纯色背景或边框样式
+- **简化或移除节假日徽章**：移除右上角的红色"休"/"班"徽章，改用更温和的视觉提示
+- **优化状态叠加逻辑**：减少多种视觉状态的冲突，确保在不同状态下节假日信息仍清晰可识别
+- **保留核心功能**：节假日识别和长按查看详情功能保持不变，仅调整视觉呈现方式
+
+## Capabilities
+
+### New Capabilities
+<!-- 无新能力 -->
+
+### Modified Capabilities
+<!-- 节假日显示规范调整 -->
+- `calendar-holiday-display`: 简化节假日视觉呈现规范，从复杂渐变+徽章样式改为简洁样式
+
+## Impact
+
+- **影响代码**: `Web/src/views/calendarV2/modules/Calendar.vue` 的样式部分（SCSS）
+- **不影响API**: 节假日数据获取逻辑保持不变
+- **不影响功能**: 节假日识别、长按提示等功能完整保留
+- **用户体验**: 提升日历界面清晰度，减少视觉干扰