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/infra/alchemy.run.ts

@@ -1,5 +1,5 @@
 import alchemy from "alchemy";
-import { TanStackStart } from "alchemy/cloudflare";
+import { Queue, TanStackStart } from "alchemy/cloudflare";
 import { config } from "dotenv";
 
 config({ path: "./.env" });
@@ -16,6 +16,10 @@ function getEnvVar(name: string): string {
 	return value;
 }
 
+const emailQueue = await Queue("email-queue", {
+	name: "kk-email-queue",
+});
+
 export const web = await TanStackStart("web", {
 	cwd: "../../apps/web",
 	bindings: {
@@ -34,7 +38,21 @@ export const web = await TanStackStart("web", {
 		MOLLIE_API_KEY: getEnvVar("MOLLIE_API_KEY"),
 		// Cron secret for protected scheduled endpoints
 		CRON_SECRET: getEnvVar("CRON_SECRET"),
+		// Queue binding for async email sends
+		EMAIL_QUEUE: emailQueue,
 	},
+	// Queue consumer: the worker's queue() handler processes EmailMessage batches
+	eventSources: [
+		{
+			queue: emailQueue,
+			settings: {
+				batchSize: 10,
+				maxRetries: 3,
+				retryDelay: 60, // seconds before retrying a failed message
+				maxWaitTimeMs: 1000,
+			},
+		},
+	],
 	// Fire every hour so reminder checks can run at 19:00 on 2026-03-15 (24h) and 18:00 on 2026-03-16 (1h)
 	crons: ["0 * * * *"],
 	domains: ["kunstenkamp.be", "www.kunstenkamp.be"],