Strobe: safety lock guardrails + audio stream cleanup

[chaosste]

Summary

• add Safety Lock mode (default ON) with 20Hz max frequency cap
• keep optional advanced mode up to 60Hz with explicit visual state
• enforce max-frequency cap in renderer for both slider and audio-reactive strobe modes
• stop microphone tracks when leaving audio mode to prevent resource leaks
• add proxy timeout handling in service wrapper

Validation

• npm run build