Builds on #23. Targets issue-6 rather than main so that PR is green before it merges.

npm run build currently fails on issue-6: tsc -b reports 14 errors and eslint . reports 6. This branch clears both without changing what the app is meant to do.

Blocking fixes

• SORT_OPTIONS was deleted but isSortOption still called it, and sort was written with an unchecked as SortOption cast. Restored the constant and put the validation back, so a broken value in session storage resets that one field as the comment promises.
• SortOption is now only id-asc and id-desc. Sorting by name would mean fetching every pokemon just to learn the names, which the fetch-on-the-fly rule does not allow.
• GetMany pushed the result of fetchSafe straight into a PokemonData[], so a failed id put a null in the list and the favorites view crashed on it. It now fetches in parallel and drops the failures.
• matchesFilter took one argument but was still called with two in GetPrevFiltered and GetNextFiltered. The rules are passed in as a parameter again, which also stops it re-reading session storage once per pokemon inside a loop that can run a thousand times.
• FavoritePokemon called .sort() and onSelectPokemon() on props typed as optional. They are required now, and the sort copies first instead of mutating the caller's array.
• Untyped index access in PokemonCard and filters.ts.
• total was reassigned during render, which the react-hooks rules reject. It is a reduce now.

Behaviour fixes

• Navigating to a new pokemon kept showing the previous one's sprite, because the sprite lived in useState and the card never remounts. It resets when the id changes.
• PokemonList and useFavorites fetched with plain useState and useEffect. Both go through TanStack Query now, so the neighbours and favorites are cached instead of refetched on every click.
• The favorite entries and the sprite toggle were div and li with onClick, so neither could be reached by keyboard. They are buttons with focus outlines.
• App rendered a second id="root" inside the one in index.html. Replaced with .app-layout.

Checks

PokemonList.test.tsx was removed in #23 and is not restored here, and GetNextFiltered / GetPrevFiltered still have no tests. Both are covered by #10.