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.

apps/web/src/router.tsx

@@ -1,3 +1,4 @@
+import type { EmailMessage } from "@kk/api/email-queue";
 import { QueryClientProvider } from "@tanstack/react-query";
 import { createRouter as createTanStackRouter } from "@tanstack/react-router";
 
@@ -6,6 +7,18 @@ import Loader from "./components/loader";
 import { routeTree } from "./routeTree.gen";
 import { orpc, queryClient } from "./utils/orpc";
 
+// Minimal CF Queue binding shape needed for type inference
+type Queue = {
+	send(
+		message: EmailMessage,
+		options?: { contentType?: string },
+	): Promise<void>;
+	sendBatch(
+		messages: Array<{ body: EmailMessage }>,
+		options?: { contentType?: string },
+	): Promise<void>;
+};
+
 export const getRouter = () => {
 	const router = createTanStackRouter({
 		routeTree,
@@ -26,3 +39,9 @@ declare module "@tanstack/react-router" {
 		router: ReturnType<typeof getRouter>;
 	}
 }
+
+declare module "@tanstack/router-core" {
+	interface Register {
+		server: { requestContext: { emailQueue?: Queue } };
+	}
+}