Typed Explorer Step 9: Validate the Boundary

Find every place your Explorer takes data from outside: the API response, the URL parameters, anything read from storage. For each, write a guard or a schema and validate it once, at the edge. Then delete every `as` and every `any` you had used to get past the compiler there. Finally, feed it a deliberately wrong response, a missing field and a string where a number belongs, and confirm the application reports it cleanly instead of crashing somewhere unrelated.