fix: Export-Encoding und Excel-Support

- CSV: UTF-8 BOM + \r\n Zeilenenden → Umlaute in Excel korrekt
- CSV: deutsche Spaltennamen, Tags als kommagetrennte Liste
- Excel (.xlsx): nativer Export via xlsx-Library mit Spaltenbreiten
- Export-Dropdown: CSV und Excel jeweils für aktuelle Ansicht und nur mit E-Mail

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

app/api/leads/export/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { prisma } from "@/lib/db";
 import { Prisma } from "@prisma/client";
+import * as XLSX from "xlsx";
 
 export async function GET(req: NextRequest) {
   try {
@@ -11,6 +12,7 @@ export async function GET(req: NextRequest) {
     const priorities = searchParams.getAll("priority");
     const hasEmail = searchParams.get("hasEmail");
     const emailOnly = searchParams.get("emailOnly") === "true";
+    const format = searchParams.get("format") || "csv"; // "csv" | "xlsx"
 
     const where: Prisma.LeadWhereInput = {};
     if (search) {
@@ -33,57 +35,86 @@ export async function GET(req: NextRequest) {
       take: 10000,
     });
 
-    const columns = [
-      "status", "priority", "company_name", "domain", "contact_name",
-      "contact_title", "email", "email_confidence", "linkedin_url", "phone",
-      "source_tab", "source_term", "tags", "country", "headcount", "industry",
-      "notes", "captured_at", "contacted_at", "serp_rank", "serp_url",
-      "serp_title", "serp_snippet", "lead_id",
-    ];
-
     const rows = leads.map(l => ({
-      status: l.status,
-      priority: l.priority,
-      company_name: l.companyName || "",
-      domain: l.domain || "",
-      contact_name: l.contactName || "",
-      contact_title: l.contactTitle || "",
-      email: l.email || "",
-      email_confidence: l.emailConfidence != null ? Math.round(l.emailConfidence * 100) + "%" : "",
-      linkedin_url: l.linkedinUrl || "",
-      phone: l.phone || "",
-      source_tab: l.sourceTab,
-      source_term: l.sourceTerm || "",
-      tags: l.tags || "",
-      country: l.country || "",
-      headcount: l.headcount || "",
-      industry: l.industry || "",
-      notes: l.notes || "",
-      captured_at: l.capturedAt.toISOString(),
-      contacted_at: l.contactedAt?.toISOString() || "",
-      serp_rank: l.serpRank?.toString() || "",
-      serp_url: l.serpUrl || "",
-      serp_title: l.serpTitle || "",
-      serp_snippet: l.serpSnippet || "",
-      lead_id: l.id,
+      "Status": l.status,
+      "Priorität": l.priority,
+      "Unternehmen": l.companyName || "",
+      "Domain": l.domain || "",
+      "Kontaktname": l.contactName || "",
+      "Jobtitel": l.contactTitle || "",
+      "E-Mail": l.email || "",
+      "E-Mail Konfidenz": l.emailConfidence != null ? Math.round(l.emailConfidence * 100) + "%" : "",
+      "LinkedIn": l.linkedinUrl || "",
+      "Telefon": l.phone || "",
+      "Quelle": l.sourceTab,
+      "Suchbegriff": l.sourceTerm || "",
+      "Tags": l.tags ? JSON.parse(l.tags).join(", ") : "",
+      "Land": l.country || "",
+      "Mitarbeiter": l.headcount || "",
+      "Branche": l.industry || "",
+      "Notizen": l.notes || "",
+      "Erfasst am": new Date(l.capturedAt).toLocaleString("de-DE"),
+      "Kontaktiert am": l.contactedAt ? new Date(l.contactedAt).toLocaleString("de-DE") : "",
+      "SERP Rang": l.serpRank?.toString() || "",
+      "SERP URL": l.serpUrl || "",
+      "SERP Titel": l.serpTitle || "",
+      "SERP Snippet": l.serpSnippet || "",
+      "Lead ID": l.id,
     }));
 
-    const csv = [
-      columns.join(","),
-      ...rows.map(r =>
-        columns.map(c => {
-          const v = String(r[c as keyof typeof r] || "");
-          return v.includes(",") || v.includes('"') || v.includes("\n")
-            ? `"${v.replace(/"/g, '""')}"`
-            : v;
-        }).join(",")
-      ),
-    ].join("\n");
+    const filename = `leadflow-vault-${new Date().toISOString().split("T")[0]}`;
+
+    if (format === "xlsx") {
+      const ws = XLSX.utils.json_to_sheet(rows);
+
+      // Column widths
+      ws["!cols"] = [
+        { wch: 14 }, { wch: 10 }, { wch: 28 }, { wch: 28 }, { wch: 22 },
+        { wch: 22 }, { wch: 32 }, { wch: 14 }, { wch: 30 }, { wch: 16 },
+        { wch: 12 }, { wch: 24 }, { wch: 20 }, { wch: 8 }, { wch: 10 },
+        { wch: 16 }, { wch: 30 }, { wch: 18 }, { wch: 18 }, { wch: 8 },
+        { wch: 40 }, { wch: 30 }, { wch: 40 }, { wch: 28 },
+      ];
+
+      const wb = XLSX.utils.book_new();
+      XLSX.utils.book_append_sheet(wb, ws, "LeadVault");
+
+      const arr = XLSX.write(wb, { type: "array", bookType: "xlsx" }) as number[];
+      const buf = new Uint8Array(arr).buffer;
+
+      return new NextResponse(buf, {
+        headers: {
+          "Content-Type": "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+          "Content-Disposition": `attachment; filename="${filename}.xlsx"`,
+        },
+      });
+    }
+
+    // CSV — UTF-8 BOM so Excel opens it correctly + \r\n line endings
+    const headers = Object.keys(rows[0] ?? {
+      "Status": "", "Priorität": "", "Unternehmen": "", "Domain": "", "Kontaktname": "",
+      "Jobtitel": "", "E-Mail": "", "E-Mail Konfidenz": "", "LinkedIn": "", "Telefon": "",
+      "Quelle": "", "Suchbegriff": "", "Tags": "", "Land": "", "Mitarbeiter": "",
+      "Branche": "", "Notizen": "", "Erfasst am": "", "Kontaktiert am": "",
+      "SERP Rang": "", "SERP URL": "", "SERP Titel": "", "SERP Snippet": "", "Lead ID": "",
+    });
+
+    const escape = (v: string) =>
+      v.includes(",") || v.includes('"') || v.includes("\n") || v.includes("\r")
+        ? `"${v.replace(/"/g, '""')}"`
+        : v;
+
+    const csv =
+      "\uFEFF" + // UTF-8 BOM — tells Excel to use UTF-8
+      [
+        headers.map(escape).join(","),
+        ...rows.map(r => headers.map(h => escape(String(r[h as keyof typeof r] ?? ""))).join(",")),
+      ].join("\r\n"); // Windows line endings for Excel
 
     return new NextResponse(csv, {
       headers: {
         "Content-Type": "text/csv; charset=utf-8",
-        "Content-Disposition": `attachment; filename="leadflow-vault-${new Date().toISOString().split("T")[0]}.csv"`,
+        "Content-Disposition": `attachment; filename="${filename}.csv"`,
       },
     });
   } catch (err) {