fix(harmonyos): stabilize remote chat and wide preview UX

[wgqqqqq]

Summary

• remove the deprecated standalone remote-session creation screen and create workspace sessions directly from the sidebar
• stabilize remote session allocation, hydration, streaming timeline projection, logout cleanup, and repeated device switching
• improve HarmonyOS tri-fold presentation: persistent master pane, three-pane code preview, expandable preview, login keyboard avoidance, and tool/thinking/subagent rendering
• add focused regression coverage for remote controllers, conversation state/presentation, event mapping, device directory, and watch provisioning
• make the time-bucket test deterministic across midnight

Verification

• pnpm run harmony:architecture
• HarmonyOS assembleHap
• HarmonyOS LocalTest
• simulator walkthrough on the HarmonyOS tri-fold target: login, remote device/workspace selection, direct session creation, Chinese streaming response, three-pane code preview, expanded preview scrolling, and return navigation

AI-assisted change; focused build, automated tests, and simulator verification completed.