Add CSV file upload and auto-delimiter detection for pilot import

Allows uploading a CSV file directly instead of only pasting text, and
auto-detects comma vs semicolon separators to support more locales.

web/api.js

@@ -48,11 +48,20 @@ const API = {
   createPilot: (id, b) => api("POST", `/api/competitions/${id}/pilots`, b),
   updatePilot: (id, pid, b) => api("PATCH", `/api/competitions/${id}/pilots/${pid}`, b),
   deletePilot: (id, pid) => api("DELETE", `/api/competitions/${id}/pilots/${pid}`),
-  importPilots: async (id, csv) => {
+  importPilots: async (id, data) => {
+    let body, headers = {};
+    if (data instanceof File) {
+      const form = new FormData();
+      form.append("file", data);
+      body = form;
+    } else {
+      headers["Content-Type"] = "text/csv";
+      body = data;
+    }
     const res = await fetch(apiURL(`/api/competitions/${id}/pilots/import`), {
       method: "POST",
-      headers: { "Content-Type": "text/csv" },
-      body: csv,
+      headers,
+      body,
       credentials: "include",
     });
     if (!res.ok) throw new Error("import_failed");