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/package.json

@@ -52,6 +52,7 @@
 	},
 	"devDependencies": {
 		"@cloudflare/vite-plugin": "^1.17.1",
+		"@tanstack/router-core": "^1.141.1",
 		"@kk/config": "workspace:*",
 		"@tanstack/react-query-devtools": "^5.91.1",
 		"@tanstack/react-router-devtools": "^1.141.1",