docs(auth): tighten V7/V8 signup note

Lead with the point reviewers found unclear: encrypted OTP verification
works with V7 signup, so moving signup to V8 can happen later.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: andrewkmin

features/authentication/otp-migration-guide.mdx

@@ -58,13 +58,12 @@ policies allow the updated activity types.
 | OTP auth | `ACTIVITY_TYPE_INIT_OTP_AUTH` (V1–V3) and `ACTIVITY_TYPE_OTP_AUTH` | `ACTIVITY_TYPE_INIT_OTP_V3`, `ACTIVITY_TYPE_VERIFY_OTP_V2`, and `ACTIVITY_TYPE_OTP_LOGIN_V2` | The flow changes. See [Migrate from the OTP auth activities](#migrate-from-the-otp-auth-activities).                       |
 
 <Note>
-  `ACTIVITY_TYPE_CREATE_SUB_ORGANIZATION_V7` accepts both legacy verification
-  tokens and the enclave-issued tokens from `VERIFY_OTP_V2`.
+  Encrypted OTP verification works with V7 signup, so you do not have to move
+  signup to V8 at the same time. `ACTIVITY_TYPE_CREATE_SUB_ORGANIZATION_V7`
+  accepts legacy and enclave-issued verification tokens.
   `ACTIVITY_TYPE_CREATE_SUB_ORGANIZATION_V8` accepts only enclave-issued tokens.
-  Moving to encrypted OTP verification does not require moving signup to V8
-  at the same time. V7 can use an enclave-issued token with a client signature.
-  Use V8 for the completed migration. Keep legacy tokens on a separate V7 path
-  during rollout. Updated SDK signup methods already submit V8.
+  Keep legacy attempts on V7 during rollout, then move all signup to V8 to
+  finish the migration. Updated SDK signup methods already submit V8.
 
 The V8 request body has the same top-level fields as V7. Each entry in
 `oauthProviders` can also take `oidcClaims` in place of `oidcToken`. The client