faster snapshot + deeper firmware timing + camera substream UI control

Three independent improvements landing together because they all
target the post-streaming-pivot "where do we spend the wall clock?"
question.

#1 — Snapshot: sharp → mediaManager native → ffmpeg cascade
pushSnapshot now tries three transforms in order of cost:
  - sharp  (~5-15ms, libvips bindings, handles resize + rotate)
  - mediaManager.convertMediaObjectToBuffer with image/jpeg;width=W
    ;height=H mime hint (~10-30ms, Scrypted's native converter,
    used only for landscape since rotation isn't standard)
  - ffmpeg one-shot (~500-700ms cold start, the old slow path)
A `path=...` field in the snapshot log identifies which transform
actually ran so the user can confirm the fast paths are reachable
in their Scrypted runtime. takePicture, transform, and POST timings
are each broken out so we can see exactly where the snapshot wall
goes.

#2 — Firmware: windowed min/avg/max breakdown + idle-gap
Stream server replaces the per-frame single-sample log with a 30-
frame window summary:
  N frames over Xs: Yfps Z MB/s avg-jpeg=KB |
    lock min/avg/max | recv min/avg/max | dec min/avg/max |
    paint min/avg/max | idle min/avg/max
- lock = mutex acquire time (sanity check; should be ~0us with one
  client owning the decoder)
- recv = body bytes off the wire
- dec  = HW JPEG decode
- paint = backbuffer flip + DMA queue
- idle = gap between previous paint completing and next header
  landing (= upstream slack). Large idle means we're waiting on
  ffmpeg/network; near-zero means we're the bottleneck.

#3 — Camera substream picker
"Stream-source choice drives end-to-end latency more than anything
else" — the existing hardcoded low-latency-first walk lands on the
camera's preview substream which is typically capped at 5-8 fps.
Adds a per-viewport setting under Display:
  Camera substream: auto | low-resolution | medium-resolution
                   | local | remote | remote-recorder
auto keeps the current behavior; the pinned options let the user
force a higher-fps source when they want stream rate > preview
rate. The chosen destination is logged at stream start.

0 files changed, 0 insertions, 0 deletions