fix(app): prevent command palette first-open flash

[opencode-agent]

Summary

• eagerly load the V2 command palette with its already code-split parent selector
• avoid the first-open Suspense fallback that blanks the session before the modal paints

Context

This follows the established fix from #35349: preserve the transition boundary and eagerly load the nested visible controls. The shared dialog API already wraps show() in startTransition; this removes the nested lazy suspension inside that transition.

Test plan

• bun typecheck in packages/app
• repository pre-push typecheck
• post-fix first-open video captured at 1280×720 with the real app UI and seeded mock OpenCode backend

Evidence

• Before/after composite