Add two new settings (both default off):
- sound_enabled: plays a short tone via Web Audio API when assistant
finishes a response or requests approval
- notifications_enabled: shows a browser notification when a response
completes while the tab is in the background
Uses Web Audio API (oscillator) instead of bundled MP3 file — zero
additional assets. Follows the standard 4-file settings pattern.
Also skip test_valid_skill_accepted when hermes-agent not installed
(skills endpoint returns 500 without the agent module).
Inspired by #176 (DavidSchuchert)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>