[codex] Add custom settings UI

[cormoran]

Summary

• Add protobuf support and a hook for cormoran_custom_settings list/write/save/discard/reset RPCs.
• Add an Advanced Settings section to Settings with section-level save/discard/reset and item-level discard/reset.
• Render layer and behavior constrained settings with device layer/behavior selectors, and add a bytecode editor modal for bytes settings.
• Extend demo mode with sample custom settings for local UI verification.

Validation

• npm run build
• npm run lint
• npm run format:check
• npm test -- --runInBand
• Browser check in demo mode for Advanced Settings, layer/behavior selectors, warning text, and bytecode editor modal.

[github-actions]

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_{Deployed from commit fe1a157}