feat: per-user volume leveling preference, synced across devices (M464 #4998)

Mode (off, auto, track, album), target (-18, -16, -14 LUFS) and boost
(within headroom, or fully with a limiter), stored per user on the server
so the web player, the Android app and casts apply the same one.

- Server: user_normalization_prefs (migration 0067), GET/PUT
  /api/me/normalization; a whole-body PUT, validated, last write wins.
- Web: Settings > Playback > Volume leveling. Saves at once, restores the
  old choice if the save fails, and caches the value for the player.
- Android: Settings card. The device keeps a copy for offline playback
  (Room v9 with an explicit migration, so the upgrade wipes nothing).
  Writes are offline-first: shown at once, PUT best effort, queued on
  failure (NORMALIZATION_SET, collapsed to the newest). A refresh never
  overwrites a change still queued.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/db/dbq/normalization_prefs.sql.go

@@ -0,0 +1,81 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: normalization_prefs.sql
+
+package dbq
+
+import (
+	"context"
+
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+const getNormalizationPrefs = `-- name: GetNormalizationPrefs :one
+SELECT mode, target_lufs, boost, updated_at
+  FROM user_normalization_prefs
+ WHERE user_id = $1
+`
+
+type GetNormalizationPrefsRow struct {
+	Mode       string
+	TargetLufs int16
+	Boost      string
+	UpdatedAt  pgtype.Timestamptz
+}
+
+func (q *Queries) GetNormalizationPrefs(ctx context.Context, userID pgtype.UUID) (GetNormalizationPrefsRow, error) {
+	row := q.db.QueryRow(ctx, getNormalizationPrefs, userID)
+	var i GetNormalizationPrefsRow
+	err := row.Scan(
+		&i.Mode,
+		&i.TargetLufs,
+		&i.Boost,
+		&i.UpdatedAt,
+	)
+	return i, err
+}
+
+const upsertNormalizationPrefs = `-- name: UpsertNormalizationPrefs :one
+INSERT INTO user_normalization_prefs (user_id, mode, target_lufs, boost)
+VALUES ($1, $2, $3, $4)
+ON CONFLICT (user_id) DO UPDATE SET
+    mode        = EXCLUDED.mode,
+    target_lufs = EXCLUDED.target_lufs,
+    boost       = EXCLUDED.boost,
+    updated_at  = now()
+RETURNING mode, target_lufs, boost, updated_at
+`
+
+type UpsertNormalizationPrefsParams struct {
+	UserID     pgtype.UUID
+	Mode       string
+	TargetLufs int16
+	Boost      string
+}
+
+type UpsertNormalizationPrefsRow struct {
+	Mode       string
+	TargetLufs int16
+	Boost      string
+	UpdatedAt  pgtype.Timestamptz
+}
+
+// Whole-row write from either client; the CHECKs in migration 0067 back the
+// handler's own validation.
+func (q *Queries) UpsertNormalizationPrefs(ctx context.Context, arg UpsertNormalizationPrefsParams) (UpsertNormalizationPrefsRow, error) {
+	row := q.db.QueryRow(ctx, upsertNormalizationPrefs,
+		arg.UserID,
+		arg.Mode,
+		arg.TargetLufs,
+		arg.Boost,
+	)
+	var i UpsertNormalizationPrefsRow
+	err := row.Scan(
+		&i.Mode,
+		&i.TargetLufs,
+		&i.Boost,
+		&i.UpdatedAt,
+	)
+	return i, err
+}