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/models.go

@@ -784,6 +784,14 @@ type UserInvite struct {
 	RedeemedBy pgtype.UUID
 }
 
+type UserNormalizationPref struct {
+	UserID     pgtype.UUID
+	Mode       string
+	TargetLufs int16
+	Boost      string
+	UpdatedAt  pgtype.Timestamptz
+}
+
 type YouMightLikeAlbum struct {
 	UserID  pgtype.UUID
 	AlbumID pgtype.UUID

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
+}

internal/db/migrations/0067_user_normalization_prefs.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS user_normalization_prefs;

internal/db/migrations/0067_user_normalization_prefs.up.sql

@@ -0,0 +1,22 @@
+-- Each user's loudness-normalization preference (M464 #4998). It is kept on
+-- the server, not per device, so the web player, the Android app and the
+-- leveled stream for UPnP/Sonos all apply the same one.
+--
+-- mode:   off, auto (album gain while an album plays in order, otherwise
+--         track gain), track or album.
+-- target: the loudness tracks are leveled to, in LUFS.
+-- boost:  headroom raises quiet tracks only as far as their true peak
+--         allows; limiter raises them all the way and limits the peaks.
+--
+-- No row means the defaults, which are the column defaults here and
+-- library.DefaultNormalizationPrefs in Go (a test holds them equal).
+CREATE TABLE user_normalization_prefs (
+    user_id     uuid PRIMARY KEY REFERENCES users(id) ON DELETE CASCADE,
+    mode        text NOT NULL DEFAULT 'auto'
+                CHECK (mode IN ('off', 'auto', 'track', 'album')),
+    target_lufs smallint NOT NULL DEFAULT -18
+                CHECK (target_lufs IN (-18, -16, -14)),
+    boost       text NOT NULL DEFAULT 'headroom'
+                CHECK (boost IN ('headroom', 'limiter')),
+    updated_at  timestamptz NOT NULL DEFAULT now()
+);

internal/db/queries/normalization_prefs.sql

@@ -0,0 +1,16 @@
+-- name: GetNormalizationPrefs :one
+SELECT mode, target_lufs, boost, updated_at
+  FROM user_normalization_prefs
+ WHERE user_id = $1;
+
+-- name: UpsertNormalizationPrefs :one
+-- Whole-row write from either client; the CHECKs in migration 0067 back the
+-- handler's own validation.
+INSERT INTO user_normalization_prefs (user_id, mode, target_lufs, boost)
+VALUES (sqlc.arg(user_id), sqlc.arg(mode), sqlc.arg(target_lufs), sqlc.arg(boost))
+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;