Add hCaptcha support alongside Turnstile and reCAPTCHA

- Add hcaptcha_site_key and hcaptcha to captcha_provider options in admin settings
- Update captcha.ts server-side verification for hCaptcha (new endpoint + secret key)
- Add hCaptcha widget rendering in register-form.tsx
- All TypeScript and Biome checks pass

src/app/admin/settings/cms-settings-config.ts

@@ -269,7 +269,7 @@ export const SETTINGS_GROUPS: SettingsGroup[] = [
 			{
 				key: "captcha_provider",
 				label: "Captcha provider",
-				description: "none | turnstile | recaptcha",
+				description: "none | turnstile | recaptcha | hcaptcha",
 				type: "text",
 				defaultValue: "none",
 			},
@@ -278,6 +278,11 @@ export const SETTINGS_GROUPS: SettingsGroup[] = [
 				label: "Turnstile site key",
 				type: "text",
 			},
+			{
+				key: "hcaptcha_site_key",
+				label: "hCaptcha site key",
+				type: "text",
+			},
 			{
 				key: "recaptcha_site_key",
 				label: "reCAPTCHA site key",