Phase 2 : dérive, ImpactScore, slider temporel

Backend :
- OpenMeteoClient : vent horaire 72h (gratuit, sans clé)
- DriftSimulationService : échantillonnage ST_GeneratePoints,
  déplacement itératif Stokes 3%, reconstruction ST_ConcaveHull,
  4 horizons H+6/12/24/48, confiance décroissante
- ImpactScoreService : score 4 composantes (distance/densité/
  vitesse/tendance), cache Redis TTL 3h, invalidation à chaque calcul
- ComputeForecastsCommand : traite les observations sans forecast
- SpotScoreController : score courant + horizons depuis forecasts

Frontend :
- TimelineSlider : navigation Now/+6h/+12h/+24h/+48h
- SargassesMap : couche observations (orange) vs forecasts (violet)
  rechargée à chaque changement d'étape
- SpotPanel : affichage score par horizon actif + indicateur confiance
- Build → backend/public/spa/

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

frontend/src/App.jsx

@@ -1,19 +1,26 @@
 import { useState } from 'react';
 import SargassesMap from './components/Map/SargassesMap';
 import SpotPanel from './components/SpotPanel/SpotPanel';
+import TimelineSlider from './components/Timeline/TimelineSlider';
 import './App.css';
 
 export default function App() {
   const [selectedSpot, setSelectedSpot] = useState(null);
+  const [activeStep,   setActiveStep]   = useState('now');
 
   return (
     <div className="app">
+      <TimelineSlider activeStep={activeStep} onChange={setActiveStep} />
+
       <SargassesMap
         onSpotSelect={setSelectedSpot}
         selectedSpotId={selectedSpot?.id}
+        activeStep={activeStep}
       />
+
       <SpotPanel
         spot={selectedSpot}
+        activeStep={activeStep}
         onClose={() => setSelectedSpot(null)}
       />
     </div>