Revert "lact: disable undervolt"

This reverts commit 6e69b40b4e.

hosts/yarn/lact.nix

@@ -27,6 +27,14 @@ in
       };
       apply_settings_timer = 5;
       gpus.${gpuId} = {
+        # ASRock RX 7800 XT (Navi 32). Voltage offset tuned via sweep with
+        # clpeak under perf=high (sustained DPM7); visible artifacting on the
+        # display engine appeared at -300 mV, so this sits 75 mV below that
+        # cliff for a real-world safety margin (cool clpeak < hot gaming).
+        voltage_offset = -120; # mV; kernel range on this card: -450..0
+        max_core_clock = 2400; # MHz; default boost ~2520
+        power_cap = 200.0; # W; default 220, max 280
+        performance_level = "auto";
       };
     };
   };