feat: audio track history

internal/model/audio_progress.go

@@ -0,0 +1,16 @@
+package model
+
+import "time"
+
+// AudioProgress is one persisted resume point for the floating audio
+// player — the last-known playback position of a single audio file for a
+// user. Key is the track URL with query/hash stripped (the stable file
+// identity, owned by the frontend). Position/Duration mirror the
+// HTMLAudioElement's currentTime/duration in seconds. UpdatedAt is set by
+// the client so multi-device writes resolve newest-wins on upsert.
+type AudioProgress struct {
+	Key       string    `json:"key"`
+	Position  float64   `json:"position"`
+	Duration  *float64  `json:"duration,omitempty"`
+	UpdatedAt time.Time `json:"updated_at"`
+}