feat: full fan control — all fans or individual fans

The fan curve previously only controlled fan index 0; secondary fans
stayed on driver control. The curve can now target all fans (new
default) or any individual fan(s).

Backend:
- hal/fans.py: get_num_fans() via nvmlDeviceGetNumFans; get_fan_info()
  returns per-fan speeds; set_fan_speed() accepts a fan index list
  (None = all fans; all-fans mode is lenient toward driver-locked
  fans, explicit lists are strict); reset_fan() restores all fans.
- server.py: per-GPU fan_targets state; the poller applies the curve to
  all target fans and logs write failures (once per distinct error);
  activation validates targets against the hardware (stale indices fall
  back to all fans); POST /api/fans accepts fans, POST /api/fans/speed
  accepts a fan index, GET /api/fans returns num_fans/fans/fan_targets.
- Persistence format is now {"curve": ..., "fans": ...}; legacy
  bare-curve entries migrate to "all fans" at startup.
- Profiles save/apply fan_targets alongside fan_curve.
- MonitoringSample carries per-fan speeds for live gauges.

Frontend:
- Fans tab: All / Fan 1 / Fan 2 / ... selector with live per-fan %;
  the selection is applied together with the curve.
- Live monitor: per-fan gauges with sparklines for multi-fan GPUs.

frontend/src/components/Fans/FanCurveEditor.tsx

@@ -2,7 +2,7 @@ import { useState, useEffect, useRef, useCallback } from "react";
 import { Check, X, RotateCcw, Plus } from "lucide-react";
 import { api } from "../../api/client.js";
 import { useCurveStore } from "../../store/curveStore.js";
-import type { FanPoint, FanState } from "../../types.js";
+import type { FanInfo, FanPoint, FanState } from "../../types.js";
 import { toast } from "sonner";
 import { ConfirmDialog } from "../common/ConfirmDialog.js";
 
@@ -44,6 +44,29 @@ function yToFan(y: number) {
   return Math.round(FAN_MAX - ((y - PAD.top) / PLOT_H) * (FAN_MAX - FAN_MIN));
 }
 
+function sameTargets(
+  a: number[] | null | undefined,
+  b: number[] | null | undefined,
+) {
+  if (a === null || a === undefined) return b === null || b === undefined;
+  if (b === null || b === undefined) return false;
+  if (a.length !== b.length) return false;
+  return a.every((v, i) => v === b[i]);
+}
+
+function fanLabel(targets: number[] | null): string {
+  return targets === null
+    ? "all fans"
+    : targets.map((i) => `Fan ${i + 1}`).join(", ");
+}
+
+const chipCls = (selected: boolean) =>
+  `px-2 py-0.5 rounded-full border text-xs font-medium transition-colors ${
+    selected
+      ? "bg-cyan-500/15 border-cyan-500/40 text-cyan-300"
+      : "bg-zinc-800 border-zinc-700 text-zinc-500 hover:text-zinc-300"
+  }`;
+
 export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
   const { selectedGpuIndex } = useCurveStore();
   const [fanState, setFanState] = useState<FanState | null>(null);
@@ -54,6 +77,9 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
   const [confirmApply, setConfirmApply] = useState(false);
   const [confirmReset, setConfirmReset] = useState(false);
   const [dragIdx, setDragIdx] = useState<number | null>(null);
+  // Fan selection: undefined = no pending change (follow server state),
+  // null = all fans, list = specific fan indices.
+  const [fanSel, setFanSel] = useState<number[] | null | undefined>(undefined);
   const svgRef = useRef<SVGSVGElement>(null);
 
   async function fetchFans() {
@@ -61,6 +87,7 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
       setLoading(true);
       const data = await api.fans(selectedGpuIndex);
       setFanState(data);
+      setFanSel(undefined);
       if (data.curve && data.curve.length > 0) {
         setPending(null);
       }
@@ -83,14 +110,41 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
   const curveActive = fanState?.curve_active ?? false;
   const isDefaults = !pending && !fanState?.curve;
 
+  const fanTargets =
+    fanSel === undefined ? (fanState?.fan_targets ?? null) : fanSel;
+  const fansChanged =
+    fanSel !== undefined && !sameTargets(fanSel, fanState?.fan_targets ?? null);
+  const fanList: FanInfo[] =
+    fanState?.fans && fanState.fans.length > 0
+      ? fanState.fans
+      : [{ index: 0, fan_pct: null }];
+
+  function toggleFan(idx: number) {
+    const numFans = fanState?.num_fans ?? 1;
+    let list: number[];
+    if (fanTargets === null) {
+      // Start from all fans, then drop the toggled one
+      list = Array.from({ length: numFans }, (_, i) => i).filter(
+        (i) => i !== idx,
+      );
+    } else {
+      list = fanTargets.includes(idx)
+        ? fanTargets.filter((i) => i !== idx)
+        : [...fanTargets, idx].sort((a, b) => a - b);
+    }
+    if (list.length === 0) return; // keep at least one fan selected
+    setFanSel(list.length === numFans ? null : list);
+  }
+
   async function handleApply() {
     const curveToApply = pending ?? fanState?.curve ?? defaultCurve();
     if (curveToApply.length < 2) return;
     setBusy(true);
     setError(null);
     try {
-      await api.updateFans(curveToApply, selectedGpuIndex);
+      await api.updateFans(curveToApply, selectedGpuIndex, fanTargets);
       setPending(null);
+      setFanSel(undefined);
       setConfirmApply(false);
       await fetchFans();
       onChanged?.();
@@ -109,6 +163,7 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
     try {
       await api.resetFans(selectedGpuIndex);
       setPending(null);
+      setFanSel(undefined);
       setConfirmReset(false);
       await fetchFans();
       onChanged?.();
@@ -251,9 +306,10 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
             <button
               onClick={() => {
                 setPending(null);
+                setFanSel(undefined);
                 setError(null);
               }}
-              disabled={!hasPending || busy}
+              disabled={(!hasPending && !fansChanged) || busy}
               className="flex items-center gap-1.5 px-2 py-1 rounded bg-zinc-800 hover:bg-zinc-700 text-zinc-300 text-xs transition-colors disabled:opacity-40 disabled:cursor-not-allowed"
             >
               <X size={12} />
@@ -270,6 +326,48 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
           </div>
         </div>
 
+        {/* Fan selection */}
+        <div className="px-4 py-2 border-b border-zinc-800/60 flex items-center gap-2 flex-wrap">
+          <span className="text-xs text-zinc-500 uppercase tracking-wider font-semibold">
+            Fans
+          </span>
+          {fanState?.num_fans === 0 ? (
+            <span className="text-xs text-zinc-600">
+              No fans available on this GPU
+            </span>
+          ) : (
+            <>
+              <button
+                onClick={() => setFanSel(null)}
+                className={chipCls(fanTargets === null)}
+                title="Control all fans"
+              >
+                All
+              </button>
+              {fanList.map((f) => (
+                <button
+                  key={f.index}
+                  onClick={() => toggleFan(f.index)}
+                  className={chipCls(
+                    fanTargets === null || fanTargets.includes(f.index),
+                  )}
+                  title={`Control Fan ${f.index + 1} with the curve`}
+                >
+                  Fan {f.index + 1}
+                  <span className="ml-1.5 font-mono text-[10px] opacity-80">
+                    {f.fan_pct !== null ? `${Math.round(f.fan_pct)}%` : "—"}
+                  </span>
+                </button>
+              ))}
+            </>
+          )}
+          {fansChanged && (
+            <span className="inline-flex items-center gap-1 px-2 py-0.5 rounded-full bg-cyan-500/15 border border-cyan-500/30 text-cyan-400 text-xs">
+              Fans: {fanLabel(fanTargets)}
+            </span>
+          )}
+        </div>
+
         {/* Error banner */}
         {error && (
           <div className="px-3 py-1.5 bg-red-900/40 border-b border-red-700 text-red-300 text-xs flex items-center justify-between">
@@ -557,13 +655,14 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
         {/* Info */}
         <div className="px-4 pb-3 text-[10px] text-zinc-600">
           {curveActive
-            ? "Fan curve is active. Server adjusts fan speed based on GPU temperature."
+            ? `Fan curve is active — controlling ${fanLabel(fanTargets)}. Server adjusts fan speed based on GPU temperature.`
             : isDefaults
               ? "These are default values. Click Apply to enable curve control, or edit points first."
               : "Apply a curve to enable automatic fan control based on temperature."}
           <span className="block mt-1 text-zinc-700">
             Drag points to adjust · click the chart to add a point · click the ✕
-            (chart or table) to remove one.
+            (chart or table) to remove one · pick which fans the curve controls
+            above.
           </span>
         </div>
       </div>
@@ -571,7 +670,7 @@ export function FanCurveEditor({ onChanged }: { onChanged?: () => void }) {
       {confirmApply && (
         <ConfirmDialog
           message="Apply fan curve?"
-          detail="Fan control will switch to curve-based mode. The server will adjust fan speed based on GPU temperature."
+          detail={`Fan control will switch to curve-based mode for ${fanLabel(fanTargets)}. The server will adjust fan speed based on GPU temperature.`}
           confirmLabel="Apply"
           onConfirm={handleApply}
           onCancel={() => setConfirmApply(false)}