Add missing post_tone_delay column migration

- Migration 027 adds post_tone_delay column to radio_systems table
- Column was referenced in code but never created in database
- Allows skipping first N seconds of audio before processing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

audio/2026/04/4_4108375_1776550757.mp3

@@ -0,0 +1 @@
+ALTER TABLE radio_systems ADD COLUMN post_tone_delay INTEGER DEFAULT 0;