fix(docs): stale future date in migration guide table (Fall 2025 has passed)

## Bug

The migration guide contains a table with a future date that has already passed.

**Affected file:** `docs/base-account/guides/migration-guide.mdx`

**Current:**
```
| User Type | Today | Future (~Fall 2025) |
```

It is now April 2026. The `Future (~Fall 2025)` column header is stale and should be updated to reflect current status.

**Proposed fix:**
Either update the column header to reflect the current state, or if the migration is now complete, simplify the table to show the current state only.