feat(users): audio_resume_rewind_seconds column

Per-user resume rewind for the audiobook/podcast player: how many
seconds (0/5/10) before the saved position playback starts, both on
open-resume and again on every genuine unpause. Motivated by the car
startup case — exact resume loses the listener's place, and the
PlaybackRequestResolver path (phone UI, Android Auto, media buttons)
all funnel through one start position.

0 = exact resume (default), so the column is inert until the profile
page sets it. Follows the default_audio_speed / keep_screen_awake
precedent: idempotent ALTER in schema.sql (re-runs on every boot),
explicit GetUser SELECT, dedicated :exec update. Handler-side strict
allow-list {0,5,10} lands with the API slice.

database/schema/schema.sql

@@ -48,6 +48,14 @@ ALTER TABLE users ADD COLUMN IF NOT EXISTS default_audio_speed REAL NOT NULL DEF
 -- mid-session. On by default; the profile page's On/Off dropdown owns it.
 ALTER TABLE users ADD COLUMN IF NOT EXISTS keep_screen_awake BOOLEAN NOT NULL DEFAULT TRUE;
 
+-- Audio resume rewind: seconds before the saved position the
+-- audiobook/podcast player starts (on open-resume AND again on every
+-- genuine unpause — the re-orientation gap, never stacked). Strict
+-- allow-list 0/5/10 enforced handler-side; 0 = exact resume. The
+-- profile page's dropdown owns it; the chapters payload carries it to
+-- every client (web + Android, incl. the car path).
+ALTER TABLE users ADD COLUMN IF NOT EXISTS audio_resume_rewind_seconds INT NOT NULL DEFAULT 0;
+
 -- Create system_settings table
 CREATE TABLE IF NOT EXISTS system_settings (
     id UUID PRIMARY KEY DEFAULT gen_random_uuid(),