app.mixin and options.mounted are not always available

[KaelWD]

useBreakpoints and useHydration add a mounted hook to every component with app.mixin, this can be disabled though: https://vuejs.org/api/compile-time-flags.html#VUE_OPTIONS_API

Vuetify wraps app.mount() instead: https://github.com/vuetifyjs/vuetify/blob/605cd8097ba60ca6bc17b5c4083128c1ff40453a/packages/vuetify/src/framework.ts#L97-L111

[johnleider]

Fixed in a355342 — replaced app.mixin with app.mount() wrapping in both useBreakpoints and useHydration, matching the pattern from Vuetify core. No longer requires __VUE_OPTIONS_API__ to be enabled.