Improve README documentation for viewer and exporter modules.

[CodeJhF]

概述

本 PR 完善了 viewer 和 exporter 模块的 README 文档。

viewer/README.md & viewer/README.zh_CN.md

• 新增功能特性列表（实时预览、图层编辑、文本编辑、图片替换、性能分析、自动更新）
• 新增环境要求说明
• 新增命令行参数文档
• 新增项目结构概览
• 新增许可证说明

exporter/README.md & exporter/README.zh_CN.md

• 新增功能特性列表（纯矢量导出、混合导出、实时预览、批量导出、导出验证、PAGViewer 集成）
• 新增菜单命令表格，展示所有 AE 菜单入口
• 新增环境要求说明
• 新增 macOS 和 Windows 平台的安装指南
• 新增项目结构概览
• 新增常见问题排查指南
• 新增许可证说明

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.00%. Comparing base (18befa6) to head (abd6e99).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3217      +/-   ##
==========================================
+ Coverage   76.97%   77.00%   +0.02%     
==========================================
  Files         413      413              
  Lines       21910    21910              
  Branches     6291     6291              
==========================================
+ Hits        16865    16871       +6     
+ Misses       3819     3816       -3     
+ Partials     1226     1223       -3     

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