feat: add Vendor Prisma model + migration

prisma/migrations/20260802232754_add_vendor/migration.sql

@@ -0,0 +1,13 @@
+-- CreateTable
+CREATE TABLE "vendors" (
+    "id" UUID NOT NULL,
+    "name" TEXT NOT NULL,
+    "contact_email" TEXT NOT NULL,
+    "contact_phone" TEXT NOT NULL,
+    "address" TEXT NOT NULL,
+    "tax_code" TEXT,
+    "notes" TEXT,
+    "created_at" TIMESTAMPTZ(6) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "vendors_pkey" PRIMARY KEY ("id")
+);