feat(graphics): detect hybrid NVIDIA+iGPU and surface GPU + DE in Diagnostics

autoconfig_graphics gains a hybrid Intel/AMD + NVIDIA branch that keeps
GSK renderer on Auto and DMA-BUF off so the iGPU handles compositing
without the dGPU getting dragged in. detect_gpu_name is exposed and
labels hybrid setups explicitly (e.g. "NVIDIA (driver 580) + Intel
(i915)"). RuntimeDiagnostics gets runtime_gpu_name and
runtime_desktop_environment so the Diagnostics panel can show what the
app sees at runtime, which is the first thing useful to triage
performance reports from log uploads.

cc

src/lib/components/DiagnosticsPanel.svelte

@@ -40,6 +40,8 @@
     runtimeIsVm: boolean;
     runtimeHwAccelEnabled: boolean;
     runtimeForceX11Active: boolean;
+    runtimeGpuName: string;
+    runtimeDesktopEnvironment: string;
     devForceDmabuf: boolean;
     envWebkitDisableDmabuf: string | null;
     envWebkitDisableCompositing: string | null;
@@ -306,9 +308,11 @@
       { label: 'GDK Scale', saved: str(diag.gfxGdkScale), runtime: '—', status: 'info' },
       { label: 'GDK DPI Scale', saved: str(diag.gfxGdkDpiScale), runtime: '—', status: 'info' },
       { label: 'Compositing Mode', saved: '—', runtime: compositing, status: 'info' },
+      { label: 'GPU', saved: '—', runtime: diag.runtimeGpuName || 'Unknown', status: 'info' },
       { label: 'GPU: NVIDIA', saved: '—', runtime: diag.runtimeHasNvidia ? 'Detected' : 'No', status: 'info' },
       { label: 'GPU: Intel', saved: '—', runtime: diag.runtimeHasIntel ? 'Detected' : 'No', status: 'info' },
       { label: 'GPU: AMD', saved: '—', runtime: diag.runtimeHasAmd ? 'Detected' : 'No', status: 'info' },
+      { label: 'Desktop Environment', saved: '—', runtime: diag.runtimeDesktopEnvironment || 'Unknown', status: 'info' },
       { label: 'Wayland', saved: '—', runtime: diag.runtimeIsWayland ? 'Yes' : 'No (X11)', status: 'info' },
       { label: 'VM', saved: '—', runtime: diag.runtimeIsVm ? 'Yes' : 'No', status: 'info' },
       { label: 'Using Fallback', saved: '—', runtime: bool(diag.runtimeUsingFallback), status: diag.runtimeUsingFallback ? 'mismatch' : 'info' },