A demo does not need a tunnel; it needs the laptop's own camera

Asked after the mobile-internet question: could a VPN let the office cameras
be shown in the demo. Three jobs get confused there and only one needs one.

Seeing the estate from anywhere already works and needs nothing - viewer mode
plus LiveHub is exactly that, outbound, no installation and no credential.

Demonstrating recognition is better done on the demo machine's own camera.
`webcam: 0` picks a capture index instead of building an RTSP URL and the
engine has supported it since the first version: CameraStore round-trips it,
source() returns the index, safe_url() reports webcam:0, and
POST /api/cameras {"id":"laptop","webcam":0} has always worked. No screen
offered it - the same gap this repo already records for the customer record
and per-camera tuning. It is now an option in the make picker, and it is the
strongest demo available: real faces, in the room, depending on no network.
A demo pointed at a camera in another building depends on two internet
connections and a tunnel staying up while somebody is talking.

The address and the index are alternatives, not extras: source() takes the
webcam first, so a half-typed host left behind would make the saved camera
describe two things and use one. The scan, the path and the camera password
are hidden for a local camera because none of them mean anything.

A tunnel is still right for one case - running the engine on a remote machine
against the office's own cameras - and still wrong for the product: it is
per-site infrastructure on every shop PC, and it gives head office
network-level access into a customer's LAN, where today we can read a
camera's picture and nothing else.

Also: installing httpx took the suite from 239 passed to 271. The HTTP tests
importorskip it so a bare checkout runs, which means the number at the bottom
of a run is not the number of tests that exist. Added to the dev extra.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj

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