Replace the 100s default HttpClient timeout (set Timeout=Infinite) with an idle/heartbeat
deadline driven by a ProgressStreamContent wrapper that reports bytes-on-the-wire. Each tick
resets the idle window and advances a MudProgressLinear per upload row. Idle window is
configurable via Upload:IdleTimeoutSeconds (default 90s).
Queue owns ordered tracks, current index, skip-fwd/back, and auto-advance via the player's TrackEnded hook; binds through Attach (no ctor growth, no service-locator). Player-bar skip controls; empty-queue play unchanged. Adds QueueService unit tests.