fix(nesdoctor): every Mac reported gpu=unknown, because the probe had no macOS arm

Seen in the macOS CI log:

  nesdoctor 0.2.2 | macos/aarch64 | gpu=unknown | ...

`gpus()` had a Linux arm, a Windows arm, and `Vec::new()` for everything else.
Macs are clients rather than hosts, so it went unnoticed -- but 0041 wants a
client vendor matrix and an unlabelled row is no use in one. An M-series
integrated GPU and a discrete Radeon in an Intel Mac decode very differently,
and "unknown" cannot tell them apart.

`system_profiler SPDisplaysDataType` is the only place the chipset name lives.
Parsed loosely: the format has changed between macOS releases, so a name we
cannot find costs a field rather than the run. Vendor is matched over Apple,
AMD, Radeon, NVIDIA and Intel; `render_node` stays `None` because macOS has
none and a Mac cannot host regardless.

Still missing on macOS and stated rather than papered over: filesystem types
and the display probe. The EDID path is sysfs on Linux and WMI on Windows, and
macOS exposes neither -- so Mac respondents report no colour depth or HDR
capability. That is a real gap for the video work, since Mac panels are exactly
the P3 and high-refresh cases worth knowing about, and it needs
`CoreDisplay`/`system_profiler` parsing rather than a one-line fix.

apps/nesdoctor/src/sys.rs

@@ -252,7 +252,50 @@ fn gpus() -> Vec<Gpu> {
         out.sort_by_key(|g| (is_virtual_adapter(&g.name), g.vendor.is_none()));
         return out;
     }
-    #[cfg(not(any(target_os = "linux", windows)))]
+    #[cfg(target_os = "macos")]
+    {
+        // Every Mac reported `gpu=unknown`, because this arm did not exist --
+        // seen in the macOS CI log. Macs are clients rather than hosts, but
+        // 0041 wants a client vendor matrix and an unlabelled entry is no use
+        // in one: an M-series integrated GPU and a discrete Radeon in an Intel
+        // Mac decode very differently.
+        //
+        // `SPDisplaysDataType` is the only place the chipset name lives.
+        // Parsed loosely on purpose: the format has changed between macOS
+        // releases and a missing name should cost a field.
+        let out = sh("system_profiler", &["SPDisplaysDataType"]).unwrap_or_default();
+        let mut gpus = Vec::new();
+        for line in out.lines() {
+            let l = line.trim();
+            if let Some(name) = l
+                .strip_prefix("Chipset Model:")
+                .or_else(|| l.strip_prefix("Chipset:"))
+            {
+                let name = name.trim();
+                if name.is_empty() {
+                    continue;
+                }
+                let up = name.to_uppercase();
+                gpus.push(Gpu {
+                    name: name.to_string(),
+                    vendor: [
+                        ("APPLE", "Apple"),
+                        ("AMD", "AMD"),
+                        ("RADEON", "AMD"),
+                        ("NVIDIA", "NVIDIA"),
+                        ("INTEL", "Intel"),
+                    ]
+                    .into_iter()
+                    .find(|(needle, _)| up.contains(needle))
+                    .map(|(_, v)| v.to_string()),
+                    // macOS has no DRM render nodes; a Mac cannot host anyway.
+                    render_node: None,
+                });
+            }
+        }
+        return gpus;
+    }
+    #[cfg(not(any(target_os = "linux", windows, target_os = "macos")))]
     return Vec::new();
 }