fix(agent): detect NVIDIA GPUs on distros without the unversioned NVML soname

On Debian and derivatives the NVIDIA driver ships only libnvidia-ml.so.1
(the unversioned symlink belongs to the dev package), and nvml-wrapper's
default init dlopens the unversioned name — so gfxinfo reported 'No GPU
found' on a fully functional RTX A2000 host while nvidia-smi worked
fine. Arch-family distros ship the symlink, which is why the desktop
never showed this.

The GPU worker now falls back to initializing NVML directly with the
versioned soname when gfxinfo's probe fails, collecting name/util/vram
through the same handle-caching path. nvml-wrapper was already in the
tree via gfxinfo — same version, no new build cost.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

socktop_agent/Cargo.toml

@@ -23,6 +23,10 @@ futures-util = "0.3.31"
 tracing = { version = "0.1", optional = true }
 tracing-subscriber = { version = "0.3", features = ["env-filter"], optional = true }
 gfxinfo = { version = "0.1.2", optional = true }
+# Direct NVML fallback for distros that ship only libnvidia-ml.so.1 (Debian
+# and derivatives) — gfxinfo's default init dlopens the unversioned name.
+# Same version gfxinfo already pulls in, so this adds no new build cost.
+nvml-wrapper = { version = "0.10", optional = true }
 once_cell = "1.19"
 axum-server = { version = "0.7", features = ["tls-rustls"] }
 rustls = { version = "0.23", features = ["aws-lc-rs"] }
@@ -35,7 +39,7 @@ time = { version = "0.3", default-features = false, features = ["formatting", "m
 
 [features]
 default = ["gpu"]
-gpu = ["gfxinfo"]
+gpu = ["gfxinfo", "nvml-wrapper"]
 logging = ["tracing", "tracing-subscriber"]
 
 [build-dependencies]