fix(kpa): a settings save must not flick the KPA500's power switch — and the maps stay under the menus

startAmps tore down and rebuilt every amplifier client on any settings
save, and closing a COM port makes the Windows driver drop DTR/RTS. On a
KPA500 those lines ARE the power switch — so 'save' meant 'amplifier off
twenty seconds later', exactly F1TPL's report, and the fix that held the
lines while OPEN couldn't survive a close. An amplifier whose config is
unchanged now keeps its running client across saves; the others still
rebuild.

Also: isolate on the FT Map panel — Leaflet's z-1000 panes were painting
over the menu bar and the Preferences dialog, as the grid map's own
comment warned.

app.go

@@ -18677,19 +18677,51 @@ func (a *App) startAmps() {
 	old := a.ampInsts
 	a.ampInsts = map[string]*ampInst{}
 	a.ampsMu.Unlock()
-	for _, inst := range old {
+	a.pgxl, a.spe, a.acom = nil, nil, nil
+	list, err := a.GetAmplifiers()
+	if err != nil {
+		for _, inst := range old {
+			go inst.stopAll()
+		}
+		return
+	}
+	// An amplifier whose configuration did not change keeps its RUNNING client
+	// across a settings save. Rebuilding closes the serial port, and closing a
+	// COM port makes the Windows driver drop DTR/RTS — which on a KPA500 is the
+	// POWER SWITCH: every save of any Settings page was switching the amplifier
+	// off (F1TPL's report). Reuse also spares the other amps a reconnect blink.
+	reused := map[string]bool{}
+	for _, c := range list {
+		if !c.Enabled {
+			continue
+		}
+		if o, ok := old[c.ID]; ok && o.cfg == c {
+			reused[c.ID] = true
+			if o.pgxl != nil && a.pgxl == nil {
+				a.pgxl = o.pgxl
+			}
+			if o.spe != nil && a.spe == nil {
+				a.spe = o.spe
+			}
+			if o.acom != nil && a.acom == nil {
+				a.acom = o.acom
+			}
+			a.ampsMu.Lock()
+			a.ampInsts[c.ID] = o
+			a.ampsMu.Unlock()
+		}
+	}
+	for id, inst := range old {
+		if reused[id] {
+			continue
+		}
 		// Stop() can block up to the dial timeout waiting for an in-progress
 		// connect; tear down in the background so saving Settings (this runs on
 		// the Wails RPC goroutine) doesn't freeze the UI.
 		go inst.stopAll()
 	}
-	a.pgxl, a.spe, a.acom = nil, nil, nil
-	list, err := a.GetAmplifiers()
-	if err != nil {
-		return
-	}
 	for _, c := range list {
-		if !c.Enabled {
+		if !c.Enabled || reused[c.ID] {
 			continue
 		}
 		isPGXL := c.Type == "" || c.Type == "pgxl"