fix(app-builder): fix SSR hydration mismatch from localStorage

[falkenbergo]

Summary

Fixes React hydration errors in the app builder when saved chat state exists in localStorage.

Previously, the server rendered the default empty state (createInitialAppState()) while the client immediately read persisted conversations on the first render, so titles, session-derived layout (main classes), and onboarding could disagree between SSR and the client.

Changes

• Seed initial state only from createInitialAppState() so the first server and client paints match.
• Restore persisted conversations, active conversation, runtime map, and onboarding (when a valid Cursor API key is saved) in useLayoutEffect after hydration.
• Rename the loader to readPersistedAppStateFromStorage() (client-only).

Testing

• Open app builder with existing localStorage data; confirm no hydration warning overlay.
• Fresh profile / cleared storage still shows default "Project 1" flow.

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Note

Low Risk
Behavior change is limited to client-side state initialization timing to prevent SSR hydration warnings; main risk is minor UI flicker/regressions in restore/onboarding state.

Overview
Fixes React hydration mismatches in AppBuilder by bootstrapping initial UI state purely from createInitialAppState() (instead of reading localStorage during initial render).

After hydration, a useLayoutEffect now restores persisted conversations/active conversation and rebuilds runtimeByConversationId, and onboarding is closed when a valid saved Cursor API key is present. The persisted-state loader is renamed/clarified as client-only via readPersistedAppStateFromStorage().

^{Reviewed by Cursor Bugbot for commit 2298e75. Bugbot is set up for automated code reviews on this repo. Configure here.}