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/models.go

@@ -640,18 +640,19 @@ type UserDashboardPreferencesGlobal struct {
 }
 
 type Users struct {
-	ID                pgtype.UUID        `db:"id" json:"id"`
-	Email             string             `db:"email" json:"email"`
-	Username          string             `db:"username" json:"username"`
-	PasswordHash      string             `db:"password_hash" json:"password_hash"`
-	FirstName         pgtype.Text        `db:"first_name" json:"first_name"`
-	LastName          pgtype.Text        `db:"last_name" json:"last_name"`
-	Role              string             `db:"role" json:"role"`
-	Theme             pgtype.Text        `db:"theme" json:"theme"`
-	MaxDevices        pgtype.Int4        `db:"max_devices" json:"max_devices"`
-	CreatedAt         pgtype.Timestamptz `db:"created_at" json:"created_at"`
-	Timezone          pgtype.Text        `db:"timezone" json:"timezone"`
-	UpdatedAt         pgtype.Timestamptz `db:"updated_at" json:"updated_at"`
-	DefaultAudioSpeed float32            `db:"default_audio_speed" json:"default_audio_speed"`
-	KeepScreenAwake   bool               `db:"keep_screen_awake" json:"keep_screen_awake"`
+	ID                       pgtype.UUID        `db:"id" json:"id"`
+	Email                    string             `db:"email" json:"email"`
+	Username                 string             `db:"username" json:"username"`
+	PasswordHash             string             `db:"password_hash" json:"password_hash"`
+	FirstName                pgtype.Text        `db:"first_name" json:"first_name"`
+	LastName                 pgtype.Text        `db:"last_name" json:"last_name"`
+	Role                     string             `db:"role" json:"role"`
+	Theme                    pgtype.Text        `db:"theme" json:"theme"`
+	MaxDevices               pgtype.Int4        `db:"max_devices" json:"max_devices"`
+	CreatedAt                pgtype.Timestamptz `db:"created_at" json:"created_at"`
+	Timezone                 pgtype.Text        `db:"timezone" json:"timezone"`
+	UpdatedAt                pgtype.Timestamptz `db:"updated_at" json:"updated_at"`
+	DefaultAudioSpeed        float32            `db:"default_audio_speed" json:"default_audio_speed"`
+	KeepScreenAwake          bool               `db:"keep_screen_awake" json:"keep_screen_awake"`
+	AudioResumeRewindSeconds int32              `db:"audio_resume_rewind_seconds" json:"audio_resume_rewind_seconds"`
 }