feat: différencier visuellement Sentinel-2 (fiable) vs Sentinel-3 (bruit)

S3 OLCI n'a pas de bande SWIR : impossible de filtrer sun glint résiduel
et aérosols sahariens → faux positifs massifs à 300 m de résolution.

- Tuiles : ajout des propriétés source/confidence/coverage_km2
- Carte : styling data-driven par source
    S2 → orange vif (#f4720a), opacité 65 % — signal confirmé
    S3 → or pâle (#d4b830), opacité 20 % — signal incertain
- Légende : entrées distinctes S2 / S3

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

backend/src/Command/GenerateTilesCommand.php

@@ -63,7 +63,11 @@ class GenerateTilesCommand extends Command
     private function queryObservationsGeoJSON(): ?string
     {
         $rows = $this->connection->fetchAllAssociative(
-            "SELECT ST_AsGeoJSON(geometry) AS geometry, COALESCE(afai_mean, 0) AS afai
+            "SELECT ST_AsGeoJSON(geometry) AS geometry,
+                    COALESCE(afai_mean, 0) AS afai,
+                    source,
+                    confidence,
+                    ROUND(COALESCE(coverage_area, 0)::numeric, 1) AS coverage_km2
              FROM sargassum_observation
              WHERE detected_at >= NOW() - INTERVAL '30 days'
                AND coverage_area > 0
@@ -71,7 +75,10 @@ class GenerateTilesCommand extends Command
         );
 
         return $this->buildFeatureCollection($rows, [
-            'afai' => static fn($r) => (float) $r['afai'],
+            'afai'        => static fn($r) => (float) $r['afai'],
+            'source'      => static fn($r) => $r['source'],          // 'Sentinel-2' | 'Sentinel-3'
+            'confidence'  => static fn($r) => (float) $r['confidence'],
+            'coverage_km2' => static fn($r) => (float) $r['coverage_km2'],
         ]);
     }