fix(build): declare @strapi/utils as peerDependency — preventive zod/v4 fix

Preventive companion to the magic-link runtime crash fix. Session
Manager did not yet crash at runtime but had the same structural
issue: @strapi/utils was being inlined into dist/server/index.js,
and @strapi/utils now internally does require('zod/v4'). With zod
pinned to ^3.x on the host the import resolves to undefined and
z.string() crashes.

Adding @strapi/utils to peerDependencies tells pack-up to emit
require('@strapi/utils') at runtime instead of copying the library
into the bundle.

Impact:
  - dist/server/index.js: 52,009 -> 13,817 lines
  - zero require('zod/v4') in bundle
  - @strapi/utils loaded at runtime from Strapi host
  - lockfile regenerated with npm install --no-workspaces

Author: Schero94

.externals.json

@@ -0,0 +1,26 @@
+{
+  "externals": [
+    "react",
+    "react-dom",
+    "react-router-dom",
+    "react-intl",
+    "styled-components",
+    "@strapi/strapi",
+    "@strapi/utils",
+    "@strapi/design-system",
+    "@strapi/icons"
+  ],
+  "output": {
+    "globals": {
+      "react": "React",
+      "react-dom": "ReactDOM",
+      "react-router-dom": "ReactRouterDom",
+      "react-intl": "ReactIntl",
+      "styled-components": "styled",
+      "@strapi/strapi": "Strapi",
+      "@strapi/utils": "StrapiUtils",
+      "@strapi/design-system": "StrapiDesignSystem",
+      "@strapi/icons": "StrapiIcons"
+    }
+  }
+}