fix(xsysinfo): read process VRAM without proc children (#12482)

* fix(xsysinfo): read process VRAM without proc children

Kernels without CONFIG_PROC_CHILDREN have no task children file, so
ProcessVRAM dropped every DRM reading. When that file is missing, walk
child processes from /proc/<pid>/stat ppid links instead. Other read
errors still drop the reading.

Fixes #12481

Signed-off-by: leilei3167 <imleilei123@gmail.com>

* docs(system): describe the proc children fallback

Document VRAM reporting on kernels without CONFIG_PROC_CHILDREN.

Assisted-by: Codex:GPT-6

---------

Signed-off-by: leilei3167 <imleilei123@gmail.com>
Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

docs/content/reference/system-info.md

@@ -40,6 +40,10 @@ 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.
 
+Kernels without `CONFIG_PROC_CHILDREN` are supported. When `/proc` does not
+provide per-thread `children` files, LocalAI finds child processes through
+the parent PIDs in `/proc/<pid>/stat`.
+
 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,