Consider adopting typed-query-selector for type-safe DOM queries

Context

From review of #5169 (comment), @sidvishnoi suggested evaluating typed-query-selector to get type-safe querySelector / querySelectorAll results without manual casts.

Current state

We use /** @type {NodeListOf<HTMLElement>} */ and similar JSDoc casts extensively across the codebase (e.g. anchor-expander.js, linter rules, link-to-dfn.js). These are unchecked at runtime and can drift from the actual selectors.

Proposal

Evaluate typed-query-selector as a dev dependency. It augments the built-in querySelector / querySelectorAll types so TypeScript infers the correct element type from the selector string (e.g. document.querySelector("a.foo") returns HTMLAnchorElement | null without a cast).

Trade-offs to consider

• Adds a dev dependency (types only, no runtime cost)
• May not cover all our selector patterns (e.g. attribute selectors, complex combinators)
• Could reduce the number of @ts-expect-error directives we need

Start by reviewing the existing JSDoc casts and selectors in anchor-expander.js, the linter rules, and link-to-dfn.js. Evaluate typed-query-selector against the selector patterns and current @ts-expect-error usage, then document whether the dependency can be adopted and which casts it would replace.