[codex] Throttle settings injector retries

[kkkayye]

Summary

• debounce settings sidebar injection retries triggered by MutationObserver churn
• throttle repeated "sidebar not found" preload logs to once every five seconds
• rebuild installer runtime assets from the updated runtime source

Root Cause

Codex settings UI mutations can fire in bursts while the settings sidebar is absent or being rebuilt. The runtime retried injection and logged every mutation, which made the preload log noisy and could waste renderer work.

Validation

• npm run build
• npm test