feat(steamdb): create in-memory cache module with 6h TTL and cooldown tracking

lib/steamdb/cache.ts

@@ -0,0 +1,51 @@
+interface CachedVersion {
+  versionString: string | null
+  buildId: string | null
+  fetchedAt: number
+}
+
+const cache = new Map<number, CachedVersion>()
+const TTL_MS = 6 * 60 * 60 * 1000 // 6 hours
+
+export function getCachedVersion(steamAppId: number): CachedVersion | null {
+  const entry = cache.get(steamAppId)
+  if (!entry) return null
+  if (Date.now() - entry.fetchedAt > TTL_MS) {
+    cache.delete(steamAppId)
+    return null
+  }
+  return entry
+}
+
+export function setCachedVersion(
+  steamAppId: number,
+  versionString: string | null,
+  buildId: string | null,
+): void {
+  cache.set(steamAppId, {
+    versionString,
+    buildId,
+    fetchedAt: Date.now(),
+  })
+}
+
+// Cooldown tracking for failed fetches
+const cooldowns = new Map<number, number>()
+
+export function isOnCooldown(steamAppId: number): boolean {
+  const until = cooldowns.get(steamAppId)
+  if (!until) return false
+  if (Date.now() > until) {
+    cooldowns.delete(steamAppId)
+    return false
+  }
+  return true
+}
+
+export function setCooldown(steamAppId: number, minutes: number = 30): void {
+  cooldowns.set(steamAppId, Date.now() + minutes * 60 * 1000)
+}
+
+export function setExtendedCooldown(steamAppId: number): void {
+  cooldowns.set(steamAppId, Date.now() + 24 * 60 * 60 * 1000) // 24 hours
+}