Feature: Implement full Internationalization (i18n) support (en/zh)

[yanghanze1]

Description

📝 Description

This PR implements full Internationalization (i18n) support for the opcode application, enabling multi-language interface capabilities. The implementation includes the integration of the react-i18next framework, complete translation resources for English and Simplified Chinese, and the migration of core components to use the new translation system.

Key Changes:

• Framework Integration: Implemented react-i18next with i18next core, including language checking and extraction tools (i18next-parser).
• Translation Resources: Created complete resource files for English (en) and Simplified Chinese (zh) across 8 functional namespaces (common, agents, projects, etc.).
• Component Migration: Migrated 62/79 (78%) of total components, including 89% of core components (e.g., AgentCard, ProjectCard, SettingsDialog).
• Type Safety: Ensured strict TypeScript compliance for all i18n hooks and keys.

🔧 Approach

1. Architecture: Adopted react-i18next for React bindings and i18next-browser-languagedetector for automatic language detection.
2. Resource Structure: Organized translations into namespaces (common, agents, settings, etc.) matching the feature modules for better maintainability.
3. Extraction: Configured i18next-parser to automate the extraction of translation keys.
4. Preservation: Technical terms like "Agent", "MCP Server", and "Checkpoint" are intentionally kept in English to maintain professional precision.

🧪 Verification & Testing

All tests passed successfully (See details in .zcf/test-reports/2026-02-01_i18n-implementation-test.md).

Test Item	Status	Result
Translation Integrity	✅	1028 keys, 100% consistent across languages
TypeScript Check	✅	0 Errors
Production Build	✅	Successful (10.89s)
Component Migration	✅	78% Overall, 89% Core
App Startup	✅	397ms, No errors

⚠️ Side Effects / Notes

• Breaking Changes: None. This is a non-breaking additive feature.
• Dependencies: Added i18next, react-i18next, i18next-browser-languagedetector, and i18next-parser (dev).
• Future Work: Remaining minor components will be migrated in subsequent updates.