feat: suivi par patch — décomposition MULTIPOLYGON avec distance et surface par patch

ST_Dump sur la dernière observation → 5 patches les plus proches dans 200km, exposés
dans /spots/{id}/score. SpotPanel affiche le nombre de patches et la distance+surface
de chacun sous forme de barres (échelle 0–100km).

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

backend/src/Controller/SpotScoreController.php

@@ -57,6 +57,7 @@ class SpotScoreController extends AbstractController
             'type'     => $spot->getType(),
             'region'   => $spot->getRegion(),
             'score'    => $current,
+            'patches'  => $this->loadPatches($id),
             'horizons' => $this->loadHorizonScores($id, $currentDistanceKm),
         ]);
     }
@@ -207,6 +208,45 @@ class SpotScoreController extends AbstractController
         ];
     }
 
+    /**
+     * Décompose la dernière observation en patches individuels (ST_Dump)
+     * et retourne les 5 plus proches du spot dans un rayon de 200 km.
+     *
+     * @return array<int, array{areaKm2: float, distanceKm: float}>|null
+     */
+    private function loadPatches(string $spotId): ?array
+    {
+        $rows = $this->connection->fetchAllAssociative(
+            'SELECT
+                ROUND(CAST(ST_Area(dump.geom::geography) / 1000000 AS numeric), 2)  AS area_km2,
+                ROUND(CAST(ST_Distance(cp.geometry::geography, dump.geom::geography) / 1000 AS numeric), 2) AS distance_km
+             FROM coastal_point cp
+             CROSS JOIN LATERAL (
+                 SELECT (ST_Dump(o.geometry)).geom AS geom
+                 FROM sargassum_observation o
+                 WHERE o.id = (
+                     SELECT o2.id FROM sargassum_observation o2
+                     INNER JOIN sargassum_forecast ff ON ff.source_observation_id = o2.id
+                     ORDER BY o2.detected_at DESC LIMIT 1
+                 )
+             ) dump
+             WHERE cp.id = :spotId
+               AND ST_Distance(cp.geometry::geography, dump.geom::geography) < 200000
+             ORDER BY distance_km ASC
+             LIMIT 5',
+            ['spotId' => $spotId]
+        );
+
+        if (empty($rows)) {
+            return null;
+        }
+
+        return array_map(
+            fn(array $r) => ['areaKm2' => (float) $r['area_km2'], 'distanceKm' => (float) $r['distance_km']],
+            $rows
+        );
+    }
+
     private function scoreToLevel(int $score): string
     {
         return match (true) {