Add setup MFA session task guide and update related documentation

- Introduced a new guide for building a custom flow for the setup MFA session task.
- Updated links in the session tasks table and MFA requirement documentation to point to the new guide.
- Made minor formatting adjustments in various documentation files for clarity.

Author: octoper

docs/_partials/session-tasks-table.mdx

@@ -6,4 +6,4 @@ The following table lists the available tasks and their corresponding keys.
 | - | - | - |
 | [Allow Personal Accounts](/docs/guides/organizations/configure#personal-accounts) | `choose-organization` | Disabled by default when enabling Organizations [for instances created after August 22, 2025](!update). When disabled, users are required to choose an Organization after authenticating. When enabled, users can choose a [Personal Account](!personal-account) instead of an Organization. |
 | [Force password reset](/docs/guides/secure/password-protection-and-rules#manually-set-a-password-as-compromised) | `reset-password` | Enabled by default [for instances created after December 8, 2025](!update). When enabled, the user is required to reset their password on their next sign-in if their password is marked as compromised. |
-| [Multi-factor authentication requirement](/docs/guides/configure/auth-strategies/sign-up-sign-in-options#multi-factor-authentication) | `setup-mfa` | When enabled, users are required to set up multi-factor authentication (MFA) after authenticating. Users can choose between authenticator app (TOTP) or SMS verification depending on which methods are enabled in the instance settings. |
+| [Multi-factor authentication requirement](/docs/guides/configure/auth-strategies/sign-up-sign-in-options#multi-factor-authentication) | `setup-mfa` | When enabled, users are required to set up multi-factor authentication (MFA) after authenticating. Users can choose between authenticator app (TOTP) or SMS verification depending on which methods are enabled in the instance settings. |

docs/guides/development/custom-flows/authentication/session-tasks.mdx

@@ -30,7 +30,7 @@ This guide demonstrates how to use the Clerk API to build a custom user interfac
   | - | - |
   | `choose-organization` | [Organization switcher guide](/docs/guides/development/custom-flows/organizations/organization-switcher) |
   | `reset-password` | [Reset password guide](/docs/guides/development/custom-flows/account-updates/forgot-password) |
-  | `setup-mfa` | [Manage TOTP-based MFA guide](/docs/guides/development/custom-flows/account-updates/manage-totp-based-mfa) or [Manage SMS-based MFA guide](/docs/guides/development/custom-flows/account-updates/manage-sms-based-mfa) {/* TODO: Update to setup-mfa custom flow guide once created */} |
+  | `setup-mfa` | [Setup MFA session task guide](/docs/guides/development/custom-flows/authentication/setup-mfa-session-task) |
 
   ## Protect routes