Refactor Sealos desktop SDK integration

[Che-Zhu]

Summary

• move Sealos Desktop SDK interaction under integrations/sealos/desktop-sdk
• remove the old lib/platform/integrations/sealos/auth compatibility layer
• require an iframe context before accepting Sealos ancestor-origin domains
• remove the current provider/ layer so future provider integration can restart from the new Sealos integration boundary
• temporarily degrade Sealos/session-dependent UI flows to ordinary unauthenticated behavior instead of importing removed providers

Verification

• pnpm build
• pnpm test
• pnpm exec tsc --noEmit
• pnpm vitest run integrations/sealos/desktop-sdk