Phase 1 : seed CoastalPoints + frontend React complet

Backend :
- SeedCoastalPointsCommand : 29 points Antilles (idempotent)
  Martinique, Guadeloupe, Sainte-Lucie, Barbade, Saint-Martin

Frontend :
- api/client.js : wrapper fetch pour spots, observations, feedback
- SargassesMap : MapLibre GL JS, marqueurs spots, couche observations
  GeoJSON avec rechargement bbox dynamique à chaque mouvement carte
- SpotPanel : Spot Mode (score/niveau/distance/trend), bouton feedback
  terrain anonyme, gestion état loading/error/null
- App.jsx : composition map + panel, état selectedSpot
- vite.config.js : proxy /api → Symfony dev, build → backend/public/spa

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

frontend/src/api/client.js

@@ -0,0 +1,39 @@
+const BASE_URL = import.meta.env.VITE_API_URL ?? '/api';
+
+async function get(path, params = {}) {
+  const url = new URL(BASE_URL + path, window.location.origin);
+  Object.entries(params).forEach(([k, v]) => v !== undefined && url.searchParams.set(k, v));
+
+  const res = await fetch(url.toString(), {
+    headers: { Accept: 'application/json' },
+  });
+
+  if (!res.ok) throw new Error(`API error ${res.status}: ${path}`);
+  return res.json();
+}
+
+async function post(path, body) {
+  const res = await fetch(BASE_URL + path, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json', Accept: 'application/json' },
+    body: JSON.stringify(body),
+  });
+
+  if (!res.ok) throw new Error(`API error ${res.status}: ${path}`);
+  return res.json();
+}
+
+export const api = {
+  spots: {
+    list: ()       => get('/spots'),
+    get:  (id)     => get(`/spots/${id}`),
+    score: (id, at) => get(`/spots/${id}/score`, { at }),
+  },
+  observations: {
+    list: (bbox, date, source) => get('/observations', { bbox, date, source }),
+    get:  (id)                 => get(`/observations/${id}`),
+  },
+  feedback: {
+    create: (data) => post('/feedback', data),
+  },
+};