add PWA installable + recalibrer scoring échelle Guadeloupe

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

frontend/public/manifest.json

@@ -0,0 +1,29 @@
+{
+  "name": "Radar Sargasses 971",
+  "short_name": "RS 971",
+  "description": "Surveillance satellite des sargasses en Guadeloupe",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#1a1a2e",
+  "theme_color": "#3ab5e6",
+  "orientation": "portrait",
+  "lang": "fr",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ],
+  "screenshots": [
+    {
+      "src": "/assets/logo-radarsargasses971.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "form_factor": "narrow",
+      "label": "Carte radar sargasses Guadeloupe"
+    }
+  ]
+}