fix(desktop): hide sessions during removal

[opencode-agent]

Summary

• add a Desktop-only session mutation overlay around the shared Solid data source
• apply pending removals when Desktop reads local or Home-query session lists
• route Desktop Home and session-timeline deletion through the overlay, restoring rows on failure and retaining successful removals until the server event lands

Desktop V2 counterpart to #44905. The shared client data layer is unchanged.

Checks

• bun typecheck (packages/app)
• focused Desktop data, Home session, and session-domain unit tests (packages/app)
• bun typecheck (packages/client)
• production benchmark attempted before and after; the existing home navigation fixture did not load its target row, so neither run emitted comparable metrics

Requested by: @Brendonovich (Brendan via Slack)