fix: causal lab — URL relative /api (pas localhost:8000)

frontend/src/pages/CausalLab.tsx

@@ -64,7 +64,7 @@ interface CalibRow {
 // ── API ───────────────────────────────────────────────────────────────────────
 
 const api = async (path: string, opts?: RequestInit) => {
-  const r = await fetch(`http://localhost:8000${path}`, opts)
+  const r = await fetch(path, opts)
   if (!r.ok) { const t = await r.text(); throw new Error(t) }
   return r.json()
 }