admin: every remote/RunPod setting is now a form field

None of this session's work had any UI, so all of it was JSON-only. Now:

MODEL PAGE — a Placement section: serve this model from a remote URL
(with its name and token on that remote), and burst-to-RunPod with the
three triggers (no free slot / queue full / no local GPU) and a target
that is either a managed pod or your own serverless endpoint. The pod
form gained engine (auto/vLLM/llama.cpp/coderai/custom), the GGUF to
download, image, health path, docker args, the private-registry
credential, the pod's bearer token with an explicit "leave it open"
opt-out, and the scaling knobs (scale-up threshold, max in-flight per
pod, sticky sessions).

SETTINGS PAGE — a remote service URL for each of the five engines
(ds4, colibri, k3, ktransformers, vLLM), the account-wide registry
credential, and a Remote capabilities card: one row per capability,
each Local / Remote URL / RunPod pod, with image, shared pool name,
VRAM, $/hr, max pods and idle timeout.

Cl...