db8d666aa1
New UserPreferences field controls the mic channel's unit on the SFM event-detail modal's waveform chart only. "dBL" default, "psi" alternate. Peaks everywhere else (tables, KPI tiles, modal summary) stay in dBL regardless — this is strictly a chart-axis preference. Surfaced as a single dropdown on Settings → General, below the auto-refresh interval. Setting up the storage half ahead of the chart port in the next commit, so the chart can read the value from /api/settings/preferences on first render instead of needing a follow-up wiring pass. Includes idempotent backend/migrate_add_mic_unit_pref.py for fleets already on an older schema. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>