feat: migrate playback module to modular domain pattern

internal/domain/playback.go

@@ -0,0 +1,18 @@
+package domain
+
+import (
+	"context"
+	"mal/internal/db"
+)
+
+type PlaybackService interface {
+	BuildWatchData(ctx context.Context, animeID int, titleCandidates []string, episode string, mode string, userID string) (map[string]any, error)
+	SaveProgress(ctx context.Context, userID string, animeID int64, episode int, timeSeconds float64) error
+}
+
+type PlaybackRepository interface {
+	GetWatchListEntry(ctx context.Context, params db.GetWatchListEntryParams) (db.WatchListEntry, error)
+	GetContinueWatchingEntry(ctx context.Context, params db.GetContinueWatchingEntryParams) (db.GetContinueWatchingEntryRow, error)
+	SaveWatchProgress(ctx context.Context, params db.SaveWatchProgressParams) error
+	UpsertContinueWatchingEntry(ctx context.Context, params db.UpsertContinueWatchingEntryParams) (db.ContinueWatchingEntry, error)
+}