feat: add language support and onboard configuration wizard (v0.2.0)

- Add language code intelligent parsing module (internal/lang)
- Support --lang parameter for target language specification
- Support multiple language code formats (BCP47, aliases, Chinese names)
- Implement interactive onboard configuration wizard
- Update Config struct with language fields
- Add survey library dependency for interactive UI
- Improve CLI command interface
- Add comprehensive unit tests for language module
- Update documentation (AGENTS.md, changelog.md, taolun.md, memory.md)

Supported language codes:
- Standard: zh-CN, zh-TW, en-US, en-GB, ja, ko, es, fr, de
- Aliases: cn, en, jp, kr, es, fr, de
- Chinese names: chinese, english, japanese

Commands:
- yoyo "Hello world" - basic translation
- yoyo --lang=cn "Hello world" - specify target language
- yoyo onboard - start configuration wizard
- yoyo onboard --force - force reconfiguration

Version: 0.2.0

configs/config.yaml

@@ -4,6 +4,8 @@
 default_provider: "siliconflow"
 default_model: "gpt-3.5-turbo"
 timeout: 30
+default_source_lang: "auto"    # 默认源语言（auto为自动检测）
+default_target_lang: "zh-CN"   # 默认目标语言（简体中文）
 
 providers:
   siliconflow: