scrypted: cut ~10s glass-to-glass latency by picking the low-latency substream + dropping queued frames

Two compounding causes of the lag:

- destination:"remote-recorder" returned the high-bitrate main encoder
  with the camera's own ~10s prebuffer baked in. Walk substreams
  low-resolution → medium-resolution → local → remote → remote-recorder
  and take the first that resolves. The low-res preview is what
  Scrypted itself uses for grid views — it's near-realtime.

- ffmpeg's output queue had no drop policy, so whenever the encode +
  push pipeline fell behind for a second the queue just kept growing,
  and we'd play back a steadily-older view of the world. Added
  -fps_mode drop so late frames hit the floor.

Plus a few input-side latency knobs (-probesize 32, -analyzeduration 0,
-avioflags direct, -fflags +discardcorrupt) so ffmpeg stops sitting
on the first chunk to probe the stream layout.

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