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/context.ts

@@ -1,13 +1,33 @@
 import { auth } from "@kk/auth";
 import { env } from "@kk/env/server";
+import type { EmailMessage } from "./email-queue";
 
-export async function createContext({ req }: { req: Request }) {
+// CF Workers runtime Queue type (not the alchemy resource type)
+type Queue = {
+	send(
+		message: EmailMessage,
+		options?: { contentType?: string },
+	): Promise<void>;
+	sendBatch(
+		messages: Array<{ body: EmailMessage }>,
+		options?: { contentType?: string },
+	): Promise<void>;
+};
+
+export async function createContext({
+	req,
+	emailQueue,
+}: {
+	req: Request;
+	emailQueue?: Queue;
+}) {
 	const session = await auth.api.getSession({
 		headers: req.headers,
 	});
 	return {
 		session,
 		env,
+		emailQueue,
 	};
 }