feat(library): sync the Steam wishlist with store prices

Each sync fetches the public wishlist and the store name, price and discount
(batches of 100) and replaces the user's wishlist_game rows, without games
the user owns. A Steam error keeps the old list, a failed store batch keeps
the last known price, and a Steam ID change drops the old account's list.
GET /api/library/wishlist returns it newest first.

src/main/resources/db/migration/V5__wishlist.sql

@@ -0,0 +1,12 @@
+-- The user's Steam wishlist without the games already owned. The sync replaces it as a whole.
+-- Name and price come from the Steam store at sync time.
+CREATE TABLE wishlist_game (
+    user_id        BIGINT       NOT NULL,
+    appid          BIGINT       NOT NULL,
+    name           VARCHAR(512),
+    added_at       TIMESTAMPTZ,
+    price          VARCHAR(32),
+    original_price VARCHAR(32),
+    discount_pct   INTEGER      NOT NULL DEFAULT 0,
+    PRIMARY KEY (user_id, appid)
+);