feat(system): report per-model DRM VRAM (#12026)

* feat(system): report per-model DRM VRAM

Expose optional resident device memory for local backend process trees.
Deduplicate DRM clients and omit unsupported or incomplete readings.
Document accounting limits and preserve a measured zero in JSON.

Closes #11970.

Assisted-by: Codex:gpt-6

* fix(system): document trusted procfs reads

Scope G304 annotations to paths built from the fixed procfs root,
integer process IDs, and kernel directory entries. These reads accept
no user-controlled path components.

Assisted-by: Codex:GPT-6 gosec

---------

Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

docs/content/reference/system-info.md

@@ -28,6 +28,29 @@ Returns available backends and currently loaded models.
 | `loaded_models[].process.memory_percent` | `number` | `rss_bytes` as a percentage of host RAM |
 | `loaded_models[].process.cpu_percent` | `number` | Share of the whole host's CPU used since the previous call, 0-100. Omitted on the first call that sees the process, because there is no earlier reading to compare against |
 | `loaded_models[].process.started_at` | `string` | When the process started (RFC 3339) |
+| `loaded_models[].size_vram` | `integer` | Optional DRM-accounted resident device memory, in bytes |
+
+### Per-model VRAM
+
+On Linux, `size_vram` reports resident device memory for the local backend
+process and its child processes. LocalAI reads `drm-resident-local*` and
+`drm-resident-vram*` from `/proc` and counts each DRM client once per GPU.
+Host-memory regions are excluded. The reading includes buffers attributed
+to the backend, without separating weights, KV cache, and other allocations.
+See the [kernel DRM accounting specification](https://docs.kernel.org/gpu/drm-usage-stats.html)
+for these counters.
+
+The field is omitted when accounting is unavailable or incomplete. This
+includes external and distributed backends, macOS, proprietary NVIDIA
+drivers, primary DRM nodes (`/dev/dri/card*`), missing resident counters,
+and unreadable process information.
+A present value of `0` means the supported counters report zero bytes.
+Treat an absent field as unknown.
+
+This is a snapshot of driver accounting, not a memory reservation. Shared
+buffers can appear in different clients' counters, and allocations can change
+during collection. Do not treat the sum across models as exclusive physical
+GPU usage. These readings do not replace capacity checks when scheduling work.
 
 ### Usage
 
@@ -49,6 +72,7 @@ curl http://localhost:8080/system
     {
       "id": "my-llama-model",
       "backend": "llama-cpp",
+      "size_vram": 5368709120,
       "process": {
         "pid": 48213,
         "rss_bytes": 5368709120,