feat(watermark): add watermark

[Wesley-0808]

🤔 这个 PR 的性质是？

• 日常 bug 修复
• 新特性提交
• 文档改进
• 演示代码改进
• 组件样式/交互改进
• CI/CD 改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他

🔗 相关 Issue

💡 需求背景和解决方案

📝 更新日志

• feat(Watermark): 新增 Watermark 水印组件

• 本条 PR 不需要纳入 Changelog

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• Changelog 已提供或无须提供

[pkg-pr-new]

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npm i https://pkg.pr.new/tdesign-miniprogram@3799

commit: e3181c9

[Copilot]

Pull Request Overview

This PR introduces a new Watermark component to add watermarks to page areas. The component supports both text and image watermarks with various customization options including positioning, rotation, opacity, and moving animations.

Key changes:

• Adds complete Watermark component implementation with TypeScript support
• Provides comprehensive examples demonstrating different watermark types and features
• Integrates watermark component into the project structure and documentation

Reviewed Changes

Copilot reviewed 35 out of 42 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/watermark/watermark.ts	Main component implementation with canvas-based watermark rendering
src/watermark/watermark.wxml	Component template with canvas and styling elements
src/watermark/utils/generateBase64Url.ts	Utility for generating base64 watermark images from canvas
src/watermark/utils/randomMovingStyle.ts	Utility for generating random animation styles for moving watermarks
src/watermark/props.ts	Component property definitions with default values
src/watermark/type.ts	TypeScript interfaces for component props and watermark content
src/watermark/_example/*	Multiple example implementations showcasing different watermark features
site/site.config.mjs	Documentation site configuration update
example/*	Example app integration and navigation updates

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[anlyyao]

FAQ:
Q: 为什么移除 wx.onThemeChange？
A: wx.onThemeChange 的引入主要是为了响应深色模式，但是只能监听到系统深/浅模式切换，其他方式的主题样式切换无法监听到。因此不如移除组件内部的 wx.onThemeChange，业务测主动调用实例的 renderWatermark() 函数，重新渲染水印组件。