feat: strategy builder

frontend/src/hooks/useApi.ts

@@ -1594,7 +1594,7 @@ export const usePriceStrategy = () =>
 
 export type OptimizeConstraints = {
   max_legs: number
-  delta_threshold: number
+  delta_threshold: number | null
   max_loss_cap?: number | null
   objective: 'net_pnl' | 'return_on_risk' | 'prob_weighted'
   top_n?: number

frontend/src/pages/StrategyBuilder.tsx

@@ -427,10 +427,11 @@ function OptimizerPanel({
           </select>
         </div>
         <div>
-          <label className="text-slate-400 block mb-1">Seuil neutralité Δ</label>
+          <label className="text-slate-400 block mb-1">Seuil neutralité Δ (optionnel)</label>
           <input
-            type="number" step={0.01} min={0} value={constraints.delta_threshold}
-            onChange={(e) => setConstraints({ ...constraints, delta_threshold: parseFloat(e.target.value) || 0 })}
+            type="number" step={0.01} min={0} placeholder="illimité"
+            value={constraints.delta_threshold ?? ''}
+            onChange={(e) => setConstraints({ ...constraints, delta_threshold: e.target.value === '' ? null : parseFloat(e.target.value) })}
             className="w-full bg-dark-700 border border-slate-700/50 rounded px-2 py-1.5 text-slate-200"
           />
         </div>