Vue 3.5: reactivity, SSR, and cleaner component authoring

Vue 3.5 is a good example of a minor release doing serious engineering work under the surface while still giving developers immediately useful features.

The release highlights are a refactored reactivity system with materially better memory usage, reactive props destructuring by default, SSR improvements like lazy hydration and `useId()`, custom element improvements, `useTemplateRef()`, deferred teleport, and `onWatcherCleanup()`.

For product teams, this is mostly about smoother authoring and fewer framework fights. For framework adopters at scale, the SSR and reactivity work is the more strategic part.