feat(email): route all email sends through Cloudflare Queue

Introduces a CF Queue binding (kk-email-queue) to decouple email
delivery from request handlers, preventing slow responses and
providing automatic retries. All send*Email calls now go through
the queue when the binding is available, with direct-send fallbacks
for local dev. Reminder fan-outs mark DB rows optimistically before
enqueueing to prevent re-enqueue on subsequent cron ticks.

packages/api/src/routers/drinkkaart.ts

@@ -9,6 +9,7 @@ import { user } from "@kk/db/schema/auth";
 import { ORPCError } from "@orpc/server";
 import { and, desc, eq, gte, lte, sql } from "drizzle-orm";
 import { z } from "zod";
+import type { EmailMessage } from "../email-queue";
 import { adminProcedure, protectedProcedure } from "../index";
 import { sendDeductionEmail } from "../lib/drinkkaart-email";
 import {
@@ -339,7 +340,7 @@ export const drinkkaartRouter = {
 				createdAt: now,
 			});
 
-			// Fire-and-forget deduction email
+			// Fire-and-forget deduction email (via queue when available)
 			const cardUser = await db
 				.select({ email: user.email, name: user.name })
 				.from(user)
@@ -348,14 +349,21 @@ export const drinkkaartRouter = {
 				.then((r) => r[0]);
 
 			if (cardUser) {
-				await sendDeductionEmail({
+				const deductionMsg: EmailMessage = {
+					type: "deduction",
 					to: cardUser.email,
 					firstName: cardUser.name.split(" ")[0] ?? cardUser.name,
 					amountCents: input.amountCents,
 					newBalanceCents: balanceAfter,
-				}).catch((err) =>
-					console.error("Failed to send deduction email:", err),
-				);
+				};
+
+				if (context.emailQueue) {
+					await context.emailQueue.send(deductionMsg);
+				} else {
+					await sendDeductionEmail(deductionMsg).catch((err) =>
+						console.error("Failed to send deduction email:", err),
+					);
+				}
 			}
 
 			return {