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.

internal/database/querier.go

@@ -894,6 +894,7 @@ type Querier interface {
 	UpdateSystemSetting(ctx context.Context, arg UpdateSystemSettingParams) error
 	// Update universal progress
 	UpdateUniversalProgress(ctx context.Context, arg UpdateUniversalProgressParams) (ReadingProgress, error)
+	UpdateUserAudioResumeRewind(ctx context.Context, arg UpdateUserAudioResumeRewindParams) error
 	UpdateUserDefaultAudioSpeed(ctx context.Context, arg UpdateUserDefaultAudioSpeedParams) error
 	UpdateUserKeepScreenAwake(ctx context.Context, arg UpdateUserKeepScreenAwakeParams) error
 	UpdateUserMaxDevices(ctx context.Context, arg UpdateUserMaxDevicesParams) (Users, error)