feat(profile): keep_screen_awake user preference (default on)

New users column surfaced as an On/Off dropdown in the profile form.
The form and API carry "true"/"false" strings with the theme-style
""-guard, so JSON clients that omit the field can't clobber it;
anything else is rejected. GET/PUT /api/auth/profile expose
keep_screen_awake alongside the other profile fields, and the reader
route threads the preference into its template metadata.

Integration tests pin the schema default, both values, omission
semantics, and rejection — dedicated test user, never testuser.

internal/database/queries.sql.go

@@ -9942,6 +9942,7 @@ SELECT
     u.updated_at,
     u.timezone,
     u.default_audio_speed,
+    u.keep_screen_awake,
     (SELECT COUNT(*) FROM devices WHERE user_id = u.id) as device_count
 FROM users u
 WHERE u.id = $1
@@ -9960,6 +9961,7 @@ type GetUserRow struct {
 	UpdatedAt         pgtype.Timestamptz `db:"updated_at" json:"updated_at"`
 	Timezone          pgtype.Text        `db:"timezone" json:"timezone"`
 	DefaultAudioSpeed float32            `db:"default_audio_speed" json:"default_audio_speed"`
+	KeepScreenAwake   bool               `db:"keep_screen_awake" json:"keep_screen_awake"`
 	DeviceCount       int64              `db:"device_count" json:"device_count"`
 }
 
@@ -9979,6 +9981,7 @@ func (q *Queries) GetUser(ctx context.Context, id pgtype.UUID) (GetUserRow, erro
 		&i.UpdatedAt,
 		&i.Timezone,
 		&i.DefaultAudioSpeed,
+		&i.KeepScreenAwake,
 		&i.DeviceCount,
 	)
 	return i, err
@@ -17236,9 +17239,23 @@ func (q *Queries) UpdateUserDefaultAudioSpeed(ctx context.Context, arg UpdateUse
 	return err
 }
 
+const UpdateUserKeepScreenAwake = `-- name: UpdateUserKeepScreenAwake :exec
+UPDATE users SET keep_screen_awake = $2, updated_at = NOW() WHERE id = $1
+`
+
+type UpdateUserKeepScreenAwakeParams struct {
+	ID              pgtype.UUID `db:"id" json:"id"`
+	KeepScreenAwake bool        `db:"keep_screen_awake" json:"keep_screen_awake"`
+}
+
+func (q *Queries) UpdateUserKeepScreenAwake(ctx context.Context, arg UpdateUserKeepScreenAwakeParams) error {
+	_, err := q.db.Exec(ctx, UpdateUserKeepScreenAwake, arg.ID, arg.KeepScreenAwake)
+	return err
+}
+
 const UpdateUserMaxDevices = `-- name: UpdateUserMaxDevices :one
 UPDATE users SET max_devices = $2, updated_at = NOW() WHERE id = $1
-RETURNING id, email, username, password_hash, first_name, last_name, role, theme, max_devices, created_at, timezone, updated_at, default_audio_speed
+RETURNING id, email, username, password_hash, first_name, last_name, role, theme, max_devices, created_at, timezone, updated_at, default_audio_speed, keep_screen_awake
 `
 
 type UpdateUserMaxDevicesParams struct {
@@ -17263,6 +17280,7 @@ func (q *Queries) UpdateUserMaxDevices(ctx context.Context, arg UpdateUserMaxDev
 		&i.Timezone,
 		&i.UpdatedAt,
 		&i.DefaultAudioSpeed,
+		&i.KeepScreenAwake,
 	)
 	return i, err
 }