Add Cap Captcha support (#2511)

* Add Cap Captcha support

- Add CaptchaCap type constant in types.go
- Add Cap struct with InstanceURL, KeyID, and KeySecret fields
- Add CapCaptcha method in provider.go to return Cap settings
- Add default settings for Cap captcha in setting.go
- Implement Cap captcha verification logic in middleware
- Expose Cap captcha settings in site API

This adds support for Cap captcha service as an alternative
captcha option alongside existing reCAPTCHA, Turnstile and
built-in captcha options.

* update cap json tags

pkg/setting/provider.go

@@ -38,6 +38,8 @@ type (
 		TcCaptcha(ctx context.Context) *TcCaptcha
 		// TurnstileCaptcha returns the Cloudflare Turnstile settings.
 		TurnstileCaptcha(ctx context.Context) *Turnstile
+		// CapCaptcha returns the Cap settings.
+		CapCaptcha(ctx context.Context) *Cap
 		// EmailActivationEnabled returns true if email activation is required.
 		EmailActivationEnabled(ctx context.Context) bool
 		// DefaultGroup returns the default group ID for new users.
@@ -638,6 +640,14 @@ func (s *settingProvider) TurnstileCaptcha(ctx context.Context) *Turnstile {
 	}
 }
 
+func (s *settingProvider) CapCaptcha(ctx context.Context) *Cap {
+	return &Cap{
+		InstanceURL: s.getString(ctx, "captcha_cap_instance_url", ""),
+		KeyID:       s.getString(ctx, "captcha_cap_key_id", ""),
+		KeySecret:   s.getString(ctx, "captcha_cap_key_secret", ""),
+	}
+}
+
 func (s *settingProvider) ReCaptcha(ctx context.Context) *ReCaptcha {
 	return &ReCaptcha{
 		Secret: s.getString(ctx, "captcha_ReCaptchaSecret", ""),