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) {

frontend/src/components/SpotPanel/SpotPanel.css

@@ -233,6 +233,56 @@
   font-weight: 400;
 }
 
+/* Patch list */
+.patch-list {
+  border-top: 1px solid rgba(0,0,0,0.08);
+  padding-top: 10px;
+  margin-top: 4px;
+}
+
+.patch-list__title {
+  margin: 0 0 8px;
+  font-size: 10px;
+  font-weight: 700;
+  text-transform: uppercase;
+  letter-spacing: .07em;
+  color: #999;
+}
+
+.patch-list__row {
+  display: grid;
+  grid-template-columns: 52px 1fr 52px;
+  align-items: center;
+  gap: 6px;
+  margin-bottom: 5px;
+}
+
+.patch-list__dist {
+  font-size: 11px;
+  font-weight: 600;
+  color: #1a1a2e;
+  text-align: right;
+}
+
+.patch-list__track {
+  height: 5px;
+  background: rgba(0,0,0,0.08);
+  border-radius: 3px;
+  overflow: hidden;
+}
+
+.patch-list__fill {
+  height: 100%;
+  background: #c47a10;
+  border-radius: 3px;
+  transition: width .5s ease;
+}
+
+.patch-list__area {
+  font-size: 11px;
+  color: #888;
+}
+
 /* Feedback */
 .spot-panel__feedback {
   border-top: 2px solid #e5e7eb;

frontend/src/components/SpotPanel/SpotPanel.jsx

@@ -140,6 +140,8 @@ export default function SpotPanel({ spot, activeStep, onClose }) {
                 </dl>
 
                 <ScoreBreakdown breakdown={displayScore.breakdown} />
+
+                {activeStep === 'now' && <PatchList patches={data?.patches} />}
               </>
             )
         )}
@@ -151,6 +153,36 @@ export default function SpotPanel({ spot, activeStep, onClose }) {
   );
 }
 
+function PatchList({ patches }) {
+  if (!patches?.length) return null;
+
+  // Échelle visuelle : 100 km = barre pleine
+  const MAX_KM = 100;
+
+  return (
+    <div className="patch-list">
+      <p className="patch-list__title">
+        {patches.length} patch{patches.length > 1 ? 'es' : ''} détecté{patches.length > 1 ? 's' : ''}
+      </p>
+      {patches.map((p, i) => {
+        const pct = Math.min((p.distanceKm / MAX_KM) * 100, 100);
+        const sizeLabel = p.areaKm2 >= 10
+          ? `${p.areaKm2} km²`
+          : `${p.areaKm2} km²`;
+        return (
+          <div key={i} className="patch-list__row">
+            <span className="patch-list__dist">{p.distanceKm} km</span>
+            <div className="patch-list__track">
+              <div className="patch-list__fill" style={{ width: `${pct}%` }} />
+            </div>
+            <span className="patch-list__area">{sizeLabel}</span>
+          </div>
+        );
+      })}
+    </div>
+  );
+}
+
 const BREAKDOWN_ITEMS = [
   { key: 'distance', label: 'Distance',  max: 40, icon: '📏' },
   { key: 'density',  label: 'Densité',   max: 30, icon: '🌿' },