Refactor pure frontend platform architecture

[yeahhe365]

Summary

• Shift the app toward a pure frontend platform architecture with a new GenAI platform seam and model catalog.
• Preserve existing persisted user data through compatibility-oriented persistence schema and migration scaffolding.
• Fix Live API integration drift, ChatInput command handling, and broaden type-safe test coverage across critical flows.

Test Plan

• npm test
• npm run build