refactor: change : to = for environment variables

Our `bundler` vite can `handle` this formatting much better.

E.g. all of these work like expected:
`NUXT_PUBLIC_X= something`
`NUXT_PUBLIC_X=something`
`NUXT_PUBLIC_X=hello world`
`NUXT_PUBLIC_X=false`
`NUXT_PUBLIC_X="false"`
`NUXT_PUBLIC_X=https://something.com?test=true`

frontend/.env-example

@@ -1,15 +1,15 @@
-NUXT_PUBLIC_API_CLIENT: ""
-NUXT_PUBLIC_LEGACY_API_CLIENT: ""
-NUXT_PRIVATE_API_SERVER: ""
-NUXT_PRIVATE_LEGACY_API_SERVER: ""
-NUXT_PUBLIC_API_KEY: ""
-NUXT_PUBLIC_DOMAIN: ""
-NUXT_PUBLIC_STRIPE_BASE_URL: ""
-NUXT_PUBLIC_LOG_IP: ""
-NUXT_PUBLIC_SHOW_IN_DEVELOPMENT: ""
-NUXT_PUBLIC_V1_DOMAIN: ""
-NUXT_PUBLIC_LOG_FILE: ""
-NUXT_PUBLIC_CHAIN_ID_BY_DEFAULT: ""
-NUXT_PUBLIC_MAINTENANCE_TS: "1717700652"
-NUXT_PUBLIC_DEPLOYMENT_TYPE: "development"
-PRIVATE_SSR_SECRET: ""
+NUXT_PRIVATE_API_SERVER=
+NUXT_PRIVATE_LEGACY_API_SERVER=
+NUXT_PUBLIC_API_CLIENT=
+NUXT_PUBLIC_API_KEY=
+NUXT_PUBLIC_CHAIN_ID_BY_DEFAULT=
+NUXT_PUBLIC_DEPLOYMENT_TYPE=development
+NUXT_PUBLIC_DOMAIN=
+NUXT_PUBLIC_LEGACY_API_CLIENT=
+NUXT_PUBLIC_LOG_FILE=
+NUXT_PUBLIC_LOG_IP=
+NUXT_PUBLIC_MAINTENANCE_TS=1717700652
+NUXT_PUBLIC_SHOW_IN_DEVELOPMENT=
+NUXT_PUBLIC_STRIPE_BASE_URL=
+NUXT_PUBLIC_V1_DOMAIN=
+PRIVATE_SSR_SECRET=