feat: API Keys via Umgebungsvariablen konfigurierbar

- Neuer getApiKey() Helper: prüft zuerst ENV-Vars, dann DB
- Alle Job-Routes nutzen getApiKey() statt direktem DB-Lookup
- Credentials-Status berücksichtigt ENV-Vars (Sidebar-Haken)
- .env.local.example: Platzhalter für alle 4 API Keys

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

app/api/credentials/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { prisma } from "@/lib/db";
 import { encrypt, decrypt } from "@/lib/utils/encryption";
+import { hasApiKeyFromEnv } from "@/lib/utils/apiKey";
 
 const SERVICES = ["anymailfinder", "apify", "vayne", "airscale", "googlemaps"] as const;
 
@@ -9,7 +10,7 @@ export async function GET() {
     const creds = await prisma.apiCredential.findMany();
     const result: Record<string, boolean> = {};
     for (const svc of SERVICES) {
-      result[svc] = creds.some(c => c.service === svc && c.value);
+      result[svc] = hasApiKeyFromEnv(svc) || creds.some(c => c.service === svc && c.value);
     }
     return NextResponse.json(result);
   } catch (err) {