Admin UI abtrennen + google settings in gui + UI enhancement

backend/prisma/migrations/20260122190000_app_setting/migration.sql

@@ -0,0 +1,12 @@
+-- CreateTable
+CREATE TABLE "AppSetting" (
+    "id" TEXT NOT NULL,
+    "key" TEXT NOT NULL,
+    "value" TEXT NOT NULL,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "AppSetting_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "AppSetting_key_key" ON "AppSetting"("key");