Embedded browser startup fix

This hotfix repairs an embedded Chromium startup regression around the CEF message pump and browser view lifecycle.

Immediate CEF work now goes through a main-queue dispatch source, page and popup callbacks are safely marshalled to the main thread, and detached browser surfaces are marked inactive instead of being torn out from under SwiftUI.

Parent Agent streaming feels alive again

Live Parent Agent output now renders through a throttled streaming text view, auto-scrolls as long answers grow, and debounces persistence so every tiny text delta does not become a disk-write fire drill.

• Added ParentAgentStreamingText for smoother live assistant output
• Added live-tail auto-scroll while an answer is still incomplete
• Debounced streaming saves and added an explicit flush path
• Cached Node runtime lookup for faster Parent Agent startup checks
• Added launch and heartbeat timing logs for future diagnostics