LightningJS 3 / Blits Conventions

Conventions, patterns, and gotchas for building TV/OTT apps with LightningJS 3 / Blits (@lightningjs/blits) in TypeScript or JavaScript — the single-file-component config object (`Blits.Component`/`Blits.Application`), its XML-style `template` string, built-in reactivity (`state`, `props`, `computed`, `watch`), remote-control `input` handling and the focus chain, the `<Layout>`/`<Text>` built-ins, `.transition` animations, and the built-in router. Use this any time the user is writing, reviewing, reading, or debugging a Blits component, template, reactive state, focus/remote-control input, transition, or route — even if they don't say "Blits" explicitly, e.g. "add a setti…