fix(amp): put the coupling switch where it can be seen

It sat above the first amplifier card. With three cards configured — the case
it exists for — that is a scroll away from anything the operator is looking at,
and it was reported as missing rather than misplaced.

Moved next to Add amplifier: coupling belongs to the SET of amplifiers, not to
any one of them, so it belongs with the other set-level control.

frontend/src/components/SettingsModal.tsx

@@ -3410,18 +3410,6 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
           {amps.length === 0 && (
             <p className="text-sm text-muted-foreground">{t('amp.none')}</p>
           )}
-          {/* Only offered with two or more: coupling one amplifier to itself is
-              a switch that cannot do anything. */}
-          {amps.length > 1 && (
-            <label className="flex items-start gap-2 text-sm cursor-pointer">
-              <Checkbox checked={ampsLinked} className="mt-0.5"
-                onCheckedChange={(c) => { setAmpsLinked(!!c); SetAmpsLinked(!!c).catch(() => {}); }} />
-              <span>
-                {t('amp.linked')}
-                <span className="block text-xs text-muted-foreground mt-0.5">{t('amp.linkedHint')}</span>
-              </span>
-            </label>
-          )}
           {amps.map((amp, i) => {
             const brand = brandOf(amp.type);
             const isPGXL = brand === 'pgxl';
@@ -3616,6 +3604,22 @@ export function SettingsModal({ onClose, onSaved, initialSection, onMainPaneChan
             <Plus className="size-3.5 mr-1" /> {t('amp.add')}
           </Button>
 
+          {/* Coupling belongs to the SET of amplifiers, not to any one of them,
+              so it sits with the other set-level control rather than above the
+              first card — where three tall cards push it out of view and it has
+              to be hunted for. Shown from two amplifiers up: coupling one to
+              itself is a switch that cannot do anything. */}
+          {amps.length > 1 && (
+            <label className="flex items-start gap-2 text-sm cursor-pointer border-t border-border/60 pt-3">
+              <Checkbox checked={ampsLinked} className="mt-0.5"
+                onCheckedChange={(c) => { setAmpsLinked(!!c); SetAmpsLinked(!!c).catch(() => {}); }} />
+              <span>
+                {t('amp.linked')}
+                <span className="block text-xs text-muted-foreground mt-0.5">{t('amp.linkedHint')}</span>
+              </span>
+            </label>
+          )}
+
         </div>
       </>
     );