Cameras on devices (openpanel C1): frames in memory, a binary uplink, demand

- Volatile frames are held in memory with a byte-bounded queue instead of
  the /dev/shm ring scanned on every put; workers keep writing to the
  directory, which is trimmed on a timer. A volatile upload no longer spools
  to disk. ARTIFACT_VOLATILE_BYTES=0 turns the ring off.
- A device sends camera frames as binary messages on its socket, held and
  published in one step and credited to its device node; refused frames are
  logged and dropped. Its snapshot carries demand and the uplink (binary, or
  http through the portal).
- One demand registry for every socket's wanted media, the tunnel's
  included, plus what running flows read, mapped onto on-demand ports and
  published as device_demand; at most 8 media names per socket.
- Per-message deflate off in serve and dev; a device may fetch the last 8
  digests of a message; published dashboards cached per store revision; a
  revoked device socket is closed with 1008.
- Media tiles want bytes only while on screen; the Devices tab previews a
  wired camera; the device node warns when a flow reads an on-demand port.

Makefile

@@ -162,7 +162,7 @@ install:  ## Install all dependencies (backend + frontend)
 	cd frontend && bun install
 
 dev-backend:  ## Start the FastAPI backend with hot-reload (local)
-	cd backend && uv run --all-extras fastapi dev fluksio/main.py
+	cd backend && uv run --all-extras uvicorn fluksio.main:app --reload --ws-per-message-deflate false
 
 dev-frontend:  ## Start the Vite dev server (local)
 	cd frontend && bun dev