Fixed signup-form dev server treating i18n as ESM (#25647)

no issue

- when running `yarn dev` in the `signup-form` app, all instances of the
form failed to render with the error:
- `Uncaught SyntaxError: The requested module
'/@fs/Users/kevin/code/Ghost/ghost/i18n/index.js' does not provide an
export named 'default' (at app.tsx:2:8)`
- the problem was that vite loads the monorepo `i18n` package using
`/@fs/` and loads it as an ESM package despite being a CommonJS package
- adding `@tryghost/i18n` to vite's `optimizeDeps` config forces the
module to be transpiled so the import works correctly

Author: kevinansfield

apps/signup-form/vite.config.mts

@@ -24,6 +24,9 @@ export default (function viteConfig() {
             allowedHosts: true, // allows domain-name proxies to the preview server
             port: 6174
         },
+        optimizeDeps: {
+            include: ['@tryghost/i18n']
+        },
         build: {
             outDir: resolve(__dirname, 'umd'),
             reportCompressedSize: false,