feat: add language support and tests for English and Chinese seed data

- Introduced a new package `seedlang` to handle language parsing and constants for English and Chinese.
- Updated `Init` functions across various modules (kb, quickreply, skill, tag) to accept a language parameter.
- Implemented English seed data for FAQs, quick replies, skills, and tags, ensuring no Chinese text is present in English data.
- Added tests to verify that English seed data does not contain Chinese characters.
- Removed outdated README file from the kb test data directory.
- Created new test files for channel and kb to validate the absence of Chinese text in English seed data.

README_ZH.md

@@ -206,7 +206,8 @@ make check          # 运行 Go 测试、前端 typecheck 和 lint
 make generator      # 执行代码生成
 make enums          # 生成前端枚举
 make migration      # 执行 migration
-make testdata       # 初始化演示/测试数据
+make testdata       # 初始化中文演示/测试数据
+make testdata TESTDATA_LANG=en  # 初始化英文演示/测试数据
 ```
 
 ## AI Agent 工作流