docs: update docs for login captcha plugin

AdminForth/778/create-login-captcha-plugin-we

Author: yaroslav8765

adminforth/documentation/docs/tutorial/09-Plugins/19-login-captcha.md

@@ -46,6 +46,39 @@ plugins: [
 ]
 ```
 
+## Preventing token reuse
+
+A captcha token stays valid at the provider for a short period, which means the same token could be replayed for several logins. To prevent this, pass an optional [key-value adapter](/docs/tutorial/Adapters/key-value-adapters) via `keyValueAdapter`. Each token is recorded once it has been used for a successful login, and any later attempt with the same token is rejected.
+
+```bash
+pnpm i @adminforth/key-value-adapter-ram
+```
+
+```ts title="./resources/adminuser.ts"
+// Import the plugin, captcha adapter and a key-value adapter
+import CaptchaPlugin from "@adminforth/login-captcha";
+import CaptchaAdapterCloudflare from "@adminforth/login-captcha-adapter-cloudflare";
+import RamKeyValueAdapter from "@adminforth/key-value-adapter-ram";
+
+...
+
+plugins: [
+    new CaptchaPlugin({
+      captchaAdapter: new CaptchaAdapterCloudflare({
+        siteKey: "YOUR_SITE_KEY", // Replace with your site key
+        secretKey: "YOUR_SECRET_KEY", // Replace with your secret key
+      }),
+      // Store used tokens to prevent them from being replayed
+      keyValueAdapter: new RamKeyValueAdapter(),
+      // Optional: how long (in seconds) a used token is remembered. Should be at least as long
+      // as the captcha provider keeps the token valid. Defaults to 300 (5 minutes).
+      tokenTimeToLiveSeconds: 300,
+    }),
+]
+```
+
+You can use any of the available [key-value adapters](/docs/tutorial/Adapters/key-value-adapters) (RAM, Redis, LevelDB or Resource-based). For multi-process or replicated deployments use a centralized adapter such as Redis, so used tokens are shared across all processes.
+
 ## Result
 
 After setting up the plugin, your login page will include a captcha. Below is an example of how it will look: