feat(header): opt-in GPU and CPU clock readings after CPU and MEM

docs/wiki/Settings-Reference.md

@@ -65,6 +65,15 @@ Manager, Attachments, File Viewer, Multi-monitor, Split, Tiles, Plan Usage, Life
 Project Insights, File Browser, Subagents, Approvals Inbox, Read My Mind, Ultracode Agents,
 Ultracode Windows, Cron.
 
+**Host readings** (opt-in, both off by default and per device): **GPU Stats** adds three items after CPU and MEM: GPU load, graphics memory and the GPU clock,
+and **CPU MHz** adds the live CPU clock. An item appears only when the
+host reports it, so a machine with no readable GPU shows nothing extra. Sources: `nvidia-smi` or the amdgpu
+sysfs files for the GPU; inside WSL, the Windows performance counters through `typeperf.exe`, which cover
+any vendor (an Intel GPU gives load and memory in use, but Windows publishes no clock for it, and its memory
+total is taken as half of Windows' RAM, the limit Windows applies to integrated GPUs); and
+`scaling_cur_freq`, `/proc/cpuinfo` or, inside WSL, the Windows `Processor Frequency` counter for the CPU
+clock. Nothing is read, and `nvidia-smi` and `typeperf.exe` are never run, while both are off.
+
 **Bottom bar** (below the chips): **Git status** shows a small indicator at the right of the
 bottom bar, off by default and per device. It reads `● N` uncommitted files, `↑ N` commits not
 pushed, `⚠ N` merge conflicts, `? N` repositories git could not read, or `✓` when everything is