add: logo top-left sur la carte, compressé à 20ko (110px)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Map/SargassesMap.css

@@ -1,3 +1,14 @@
+/* ── Logo ── */
+.smap-logo {
+  position: absolute;
+  top: 12px;
+  left: 12px;
+  width: 110px;
+  pointer-events: none;
+  z-index: 5;
+  filter: drop-shadow(1px 2px 3px rgba(0,0,0,0.25));
+}
+
 /* ── Indicateur fraîcheur données ── */
 .smap-freshness {
   position: absolute;

frontend/src/components/Map/SargassesMap.jsx

@@ -271,6 +271,8 @@ export default function SargassesMap({ onSpotSelect, selectedSpotId, activeStep,
     >
       <NavigationControl position="bottom-right" />
 
+      <img src="/assets/logo-radarsargasses971.png" className="smap-logo" alt="Radar Sargasses 971" />
+
       {dataDate && (
         <div className="smap-freshness">
           Données du {dataDate.toLocaleDateString('fr-FR', { day: '2-digit', month: '2-digit' })}