runpod: place any model individually, keep orchestration local, ship LoRAs

PER-MODEL PLACEMENT FOR ANY KIND. Sending a model to RunPod used to work
only for text: resolve_pod_engine looked at whether the path ended in
.gguf, and RunpodBackend implements chat only. A diffusion model pinned
to runpod would have been handed to vLLM, which cannot serve it. Now the
model's OWN KIND picks the pod: an image/video/TTS/STT/embedding model
gets that capability's published coderai image, a GGUF gets llama.cpp, an
HF repo gets vLLM. The gateway routes by model BEFORE capability, so two
models of the same kind can differ — one video model pinned local with
`placement: "local"` while another runs on its own pod with its own
budget, which capability-level routing could never express.

A pod rented for one model starts with an EMPTY catalogue and would
refuse every request for it, so pod_plan seeds CODERAI_SEED_MODELS with
that model's entry and the pod registers it at startup (in memory only —
a pod is disposable, and writing it would surprise anyone setting the
variable on a real install). Only fields that describe the model travel:
never local paths, which mean nothing there, and never this deployment's
placement settings, which would have the pod renting pods of its own.

ORCHESTRATION STAYS LOCAL. /v1/pipelines, /v1/characters and
/v1/environments are no longer gatewayable capabilities. They are a
sequence of calls to other endpoints, and they already dispatch each step
through the front as its own /v1 request — so every step is placed by its
own model's config, and a chain can mix local and remote freely.
Forwarding the chain would have moved the logic to a pod and placed every
step by that pod's catalogue instead.

LORAS FOLLOW THE REQUEST. A LoRA is a file on this machine; a pod has
never seen it. The blob store is content-addressed, so each adapter is
hashed, checked against the remote's /v1/loras/blob/<hash>, uploaded only
when missing, and the reference rewritten to that id — repeat requests
upload nothing. QLoRA needs nothing extra: the quantisation is in how the
base model loads, the adapter is the same safetensors file. An HF id or
URL is left alone for the remote to fetch.

Also: a vLLM pod now refuses a local model path up front, with the same
reasoning as the GGUF guard — otherwise it boots for minutes and dies —
and passes `quantization` through, since a local load_in_4bit does not
carry over to vLLM.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY