Portal: add nullable System Name to LicenseKey with per-account unique index

Adds systemName (as typed, trimmed) and systemNameLower (case-folded) to
LicenseKey plus a unique index on (userId, systemNameLower) so names are
case-insensitively unique per account when non-null. Additive and
reversible; migration tested up/down. Regenerates the Prisma client.

prisma/migrations/20260929120000_add_license_key_system_name/migration.sql

@@ -0,0 +1,6 @@
+-- AlterTable
+ALTER TABLE "LicenseKey" ADD COLUMN     "systemName" TEXT,
+ADD COLUMN     "systemNameLower" TEXT;
+
+-- CreateIndex
+CREATE UNIQUE INDEX "LicenseKey_userId_systemNameLower_key" ON "LicenseKey"("userId", "systemNameLower");