Adds a collapsible "🎲 Seed Finder" panel to the voice inspector pane.
Select a voice, expand the panel, set a seed range (default 1–15), and
click Run to generate audio samples with different seeds.
Each result row has Play and "Use this seed" buttons. "Use this seed"
saves the chosen seed to the faster-qwen3-tts voices.json via the new
/api/tts-voice-seed proxy endpoint (which calls /voice-seed on the TTS
server). The saved row gets a ✓ marker.
Test sentence auto-selects DE/EN mixed or EN-only based on voice name.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
