Expose per-model memory usage (the per-process VRAM walk already computes it, then discards the split)

Is your feature request related to a problem? Please describe.
There is no way to ask LocalAI how much memory each loaded model holds, so a
downstream scheduler cannot split a shared GPU into "what the engine holds" and
"what everything else holds".

I run chat, embeddings, transcription and image generation through one LocalAI
container on one consumer card, and admit background work only when there is room
left for a user's request. Without a per-model figure that subtraction is
unavailable and background work has to be admitted unweighed.

Checked on v4.9.0 (f7ad3f70eb5d8a0ddf80e08557f0d7df28cf032e), image
localai/localai:v4.9.0-gpu-nvidia-cuda-12, RTX 3060, two models resident:

• GET /system — ids and backend names only, no figures.
• GET /api/ps — size and size_vram are literal 0. Filed separately as a bug.
• GET /backend/monitor?model=granite-4.1-8b — 500 here, and gopsutil RSS/VMS
  is host process memory rather than device memory even when it works:
  rpc error: code = Unimplemented desc = , then failed local node process sample: no grpc backend found for llama-cpp/models/granite-4.1-8b/granite-4.1-8b-Q4_K_M.gguf.bin
• GET /api/resources — device aggregate and per-GPU totals, which is genuinely
  useful and I'll switch to it, but it cannot attribute usage to a model.
• POST /api/models/vram-estimate — a prediction from weight files, not a reading.
  It can't see the actual offload split, and being wrong in the optimistic
  direction is what crashes the box.
• GET /metrics — Go runtime metrics only.

Describe the solution you'd like
Per-model resident memory on /system, as optional per-entry fields:

{"loaded_models":[{"id":"granite-4.1-8b","backend":"llama-cpp","size_vram":5100000000}]}

Omitting the field (or null) where a backend can't report it is much better than 0,
for the reason in the linked bug. Weights alone would already be a large improvement
over nothing; a KV-cache split would be ideal but isn't required. /system vs. a new
endpoint vs. populating /api/ps — no preference, whichever fits the API surface.

Most of the machinery looks like it's already there on Linux. drmFdInfoUsageByRenderNode
walks /proc/[0-9]*/fd for DRM render fds and reads drm-total-<region> per PID:

https://github.com/mudler/LocalAI/blob/v4.9.0/pkg/xsysinfo/drmfdinfo.go#L48-L78

but then does out[renderName] += ..., aggregating per GPU and dropping the per-PID
breakdown. Since each backend is its own gRPC process, keeping the PID key and joining
it against the loaded-model list would give per-model VRAM with no new probing. That
path covers amdgpu/i915/xe on kernel >= 5.19 and not NVIDIA's proprietary driver, which
doesn't emit those keys — which is exactly why I'm asking for an optional per-entry
field rather than a guaranteed one. Please don't let uneven backend support block it:
partial coverage that says so is far more useful than none.

Describe alternatives you've considered

• nvidia-smi --query-compute-apps — can't work across vendors, which is a large part
  of why LocalAI is attractive here. It also returns no rows at all in-container on a
  WSL2 host, while the card correctly reports 10849/12288 MiB used.
• Summing /backend/monitor — rejected even with the 500 fixed: host RSS/VMS says
  nothing about VRAM and double-counts mapped weights.
• Trusting /api/ps — would over-commit the card, per the linked bug.
• Aggregate device reading plus a measured "everything else" peak — what I do today.
  It works but is coarse: the engine's own share is never known.
• Estimating from the GGUF plus a modelled KV cache, i.e. what vram-estimate does —
  a guess wearing a measurement's clothes, and wrong in the direction that crashes.

Additional context
Searched existing issues for size_vram, api/ps, GPUMemoryInfo and vram-in-title and found nothing covering this. I'm not able to take the PR, but happy to test a change against this setup and to report what each backend does or doesn't report.

Written by my beloved Claude Code :)

Start with pkg/xsysinfo/drmfdinfo.go, especially drmFdInfoUsageByRenderNode and its /proc DRM fd walk, then trace how /system assembles loaded model entries. Determine how the per-PID information can be associated with loaded backend processes without changing unsupported-driver behavior. Done means /system can expose an optional per-model memory field, omitting it when unavailable, with existing aggregate reporting preserved.