docs(portal): add domain config keys to reference and anchor links in B16

- Add PORTAL_DOMAIN_ENABLE_CUSTOM and PORTAL_DOMAIN_DEFAULT entries to
  the configuration reference with type, config file key, and description
- Update B16 config table links to point directly to those anchors

Author: sharadregoti

portal/install/custom-domain.mdx

@@ -34,8 +34,8 @@ Two configuration keys control custom domain behavior:
 
 | Config Key | Description |
 | :--------- | :---------- |
-| [`Domain.EnableCustomDomains`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration) | Enables custom domain support. Set to `true`. Env var: `PORTAL_DOMAIN_ENABLE_CUSTOM`. |
-| [`Domain.DefaultDomain`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration) | The domain consumers use to access the Live Portal, for example `developers.mycompany.com`. Env var: `PORTAL_DOMAIN_DEFAULT`. |
+| [`Domain.EnableCustomDomains`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration#portal-domain-enable-custom) | Enables custom domain support. Set to `true`. Env var: `PORTAL_DOMAIN_ENABLE_CUSTOM`. |
+| [`Domain.DefaultDomain`](/product-stack/tyk-enterprise-developer-portal/deploy/configuration#portal-domain-default) | The domain consumers use to access the Live Portal, for example `developers.mycompany.com`. Env var: `PORTAL_DOMAIN_DEFAULT`. |
 
 Add these to your Portal configuration. For how to pass environment variables in your deployment type, see the install guide for [Docker](/portal/install/docker), [Kubernetes](/portal/install/kubernetes), or [Linux](/portal/install/linux).
 

product-stack/tyk-enterprise-developer-portal/deploy/configuration.mdx

@@ -285,6 +285,16 @@ You can specify any string value in this setting. Omit this setting if you don't
 **Type:** `string` <br/>
 **Description**: Redirects the portal login page to a custom SSO login URL. When set, GET requests to `/auth/password/login` are automatically redirected to this URL, and the portal's "Log in" button points to it. This is useful when using an Identity Provider (IDP) based login/SSO profile, as it allows you to bypass the default portal password login page and direct users to your external IDP login page instead. This setting only affects the login page redirect; user registration and password reset pages remain unchanged.
 
+### PORTAL_DOMAIN_ENABLE_CUSTOM
+**Config file:** Domain.EnableCustomDomains <br/>
+**Type:** `boolean` <br/>
+**Description**: Enables custom domain support for the Developer Portal. When set to `true`, the portal uses the domain specified in `PORTAL_DOMAIN_DEFAULT` as the public-facing URL for the Live Portal instead of inferring it from incoming request headers. The default value is `false`.
+
+### PORTAL_DOMAIN_DEFAULT
+**Config file:** Domain.DefaultDomain <br/>
+**Type:** `string` <br/>
+**Description**: The custom domain that API consumers use to access the Live Portal, for example `developers.mycompany.com`. This setting takes effect only when `PORTAL_DOMAIN_ENABLE_CUSTOM` is set to `true`.
+
 ## Response Headers Configuration
 This section explains how to configure custom HTTP response headers that will be added to all responses from the Portal.