Add RCON client + SendCurrency service (AtomCMS-faithful)

- rcon.ts: Node net.Socket transport speaking AtomCMS's exact protocol (raw
  JSON {"key","data"} over rcon_ip:rcon_port, fire-and-forget) with a bounded
  timeout + backoff retry; typed commands matching RconService EXACTLY
  (sendgift `itemid`, disconnect `username`, no-data => data:null, givepoints
  numeric `type`, forwarduser, setmotto/setrank/alertuser, give*). Injectable
  transport keeps command shapes unit-testable.
- send-currency.ts: mirrors the SendCurrency action — RCON deliver, else DB
  fallback (credits -> users.credits; duckets/diamonds/points -> users_currency
  by type 0/5/101).
- env: RCON_HOST/PORT/TIMEOUT/RETRIES. vitest: SKIP_ENV_VALIDATION for unit tests.

Verified: tsc exit 0, vitest 39/39, next build exit 0. Live TCP test deferred
(needs a running emulator).

src/lib/services/send-currency.ts

@@ -0,0 +1,82 @@
+import type { RconClient } from "@/lib/services/rcon";
+
+export type CurrencyName = "credits" | "duckets" | "diamonds" | "points";
+
+// users_currency.type values for the non-credits currencies.
+const TYPE_VALUE: Record<Exclude<CurrencyName, "credits">, number> = {
+  duckets: 0,
+  diamonds: 5,
+  points: 101,
+};
+
+export interface CurrencyDb {
+  user: {
+    update(args: {
+      where: { id: number };
+      data: { credits: { increment: number } };
+    }): Promise<unknown>;
+  };
+  usersCurrency: {
+    upsert(args: {
+      where: { userId_type: { userId: number; type: number } };
+      update: { amount: { increment: number } };
+      create: { userId: number; type: number; amount: number };
+    }): Promise<unknown>;
+  };
+}
+
+export interface SendCurrencyDeps {
+  rcon: Pick<RconClient, "giveCredits" | "giveDuckets" | "giveDiamonds" | "givePointsGotw">;
+  db: CurrencyDb;
+}
+
+/**
+ * Mirrors AtomCMS's SendCurrency action: deliver via RCON, falling back to a
+ * direct DB write when RCON delivery fails (the PHP version checks
+ * rcon->isConnected up front; trying-then-falling-back is equivalent and more
+ * robust). Credits live on users.credits; duckets/diamonds/points live in
+ * users_currency keyed by (user_id, type).
+ */
+export async function sendCurrency(
+  deps: SendCurrencyDeps,
+  userId: number,
+  type: CurrencyName,
+  amount: number | null | undefined,
+): Promise<boolean> {
+  if (!amount || amount <= 0) return false;
+
+  if (await rconDeliver(deps.rcon, userId, type, amount)) return true;
+
+  if (type === "credits") {
+    await deps.db.user.update({
+      where: { id: userId },
+      data: { credits: { increment: amount } },
+    });
+  } else {
+    const t = TYPE_VALUE[type];
+    await deps.db.usersCurrency.upsert({
+      where: { userId_type: { userId, type: t } },
+      update: { amount: { increment: amount } },
+      create: { userId, type: t, amount },
+    });
+  }
+  return true;
+}
+
+function rconDeliver(
+  rcon: SendCurrencyDeps["rcon"],
+  userId: number,
+  type: CurrencyName,
+  amount: number,
+): Promise<boolean> {
+  switch (type) {
+    case "credits":
+      return rcon.giveCredits(userId, amount);
+    case "duckets":
+      return rcon.giveDuckets(userId, amount);
+    case "diamonds":
+      return rcon.giveDiamonds(userId, amount);
+    case "points":
+      return rcon.givePointsGotw(userId, amount);
+  }
+}