Path of Exile 2 Shop API

Add itemshop.gg's Item Shop API to this project. Full reference: https://itemshop.gg/developers (read it if you can fetch pages).

The game I'm building for is Path of Exile 2 (slug "path-of-exile-2"): its shop is https://itemshop.gg/api/v1/shop/path-of-exile-2.


Authentication
- Every request needs an API key, sent as the header "Authorization: Bearer <key>".
- Read the key from an environment variable named ITEMSHOP_API_KEY. Never hard-code it, commit it, or send it to a browser: call the API from server-side code only. If this project has an example env file, add ITEMSHOP_API_KEY to it with a placeholder.
- I make keys at https://itemshop.gg/account#api. If the variable isn't set, fail with a clear message saying so.

Endpoints (all GET, all JSON shaped { data, meta })
- https://itemshop.gg/api/v1/games: every game covered, with slug, name, page url, currency, reset time (UTC) and whether item history is available (itemHistory).
- https://itemshop.gg/api/v1/shop/{game}: the shop on sale now, as sections of items.
- https://itemshop.gg/api/v1/rotations: a fingerprint per game that changes when its shop changes. Poll this, and fetch a shop only when its fingerprint moves.
- https://itemshop.gg/api/v1/history/{game}: the days that game's shop changed, newest first.
- https://itemshop.gg/api/v1/history/{game}/{YYYY-MM-DD}: the shop on that day (UTC), same shape as /shop, plus shopDate and exact.
- https://itemshop.gg/api/v1/items/{game}/{itemKey}: one item and its stays in the shop. itemKey comes from items in shop or history answers.
Game slugs: valorant, marvel-rivals, overwatch, diablo-4, call-of-duty, rainbow-six-siege, aniimo, apex-legends, arc-raiders, battlefield-6, dead-by-daylight, war-thunder, pubg, once-human, league-of-legends, teamfight-tactics, path-of-exile-2, sea-of-thieves, wardogs, discord, rust.

The shop answer
- data: { game, shopDate, updatedAt, expiresAt, stale, itemCount, sections: [{ title, upcoming, endsAt, items }] }.
- Each item: { id, itemKey, name, type, rarity: { name, color } | null, price: { amount, label, currency, currencyIcon, regular }, images: { card, render }, badge, availability: { from, until, untilLabel }, bundle, contents: [...], soldOut, sourceUrl }.
- Many fields can be null; handle that. price.amount is null when the store shows no number, and price.label then holds a word such as "Included". price.currency is the game currency's name, or an ISO code like "USD" for real money. Sections with upcoming: true can't be bought yet. An empty sections list with stale: false is a genuinely empty shop.
- Write types for these shapes in this project's language.

Being a good client
- Cache answers: shops change every few minutes at most, and an answer is good for about two minutes. Send back the ETag as If-None-Match and treat 304 as "unchanged".
- The limit is 600 requests a minute per key. On 429, wait for the Retry-After header's seconds before trying again.
- Errors are { error: { code, message } }. Handle 401 (key_required or invalid_key: the key is missing, wrong or revoked), 404 (unknown_game, not_recorded, unknown_item, no_items), 429 and 503 (try again later).
- Set a User-Agent header that names this project.

Required by the terms
- Wherever the data is shown, show a visible link: "Data from itemshop.gg", linking to meta.attribution.url from the answer. Add it to the UI you build.

Start by asking me what I want built with it (for example a Discord bot command, a site widget or a daily post), unless I've already said, then implement it following the existing patterns in this codebase.