Cloud getting-started §2 "Verifying your email address" is circular and omits the custom-domain caveat

## What

`content/en/cloud/getting-started/getting-started-with-layer5-account.md` §2
("Verifying your email address") has no actual instructions, and its one
sentence refers the reader to the section they are already reading:

```markdown
### 2. Verifying your email address

To ensure you can use all the features in your Layer5 plan, verify your email
address after signing up for a new account. For more information, see
"Verifying your email address."
```

That circular reference should become real content, and there is a
custom-domain caveat that currently appears nowhere.

## Why now

layer5io/meshery-cloud#6092: on a tenant custom domain (e.g. `cloud.meshery.io`)
the verification link in the signup email could not be completed. The email was
correct — correctly branded, correctly addressed at the tenant host — but
clicking it redirected to the provider's `/error` page. Fixed in meshery-cloud;
the user-visible consequences want documenting.

## Suggested content for §2

1. **What the email contains** — a verification code and a link; either
completes verification.
2. **Custom domains** — the link now keeps you on your organization's own
domain end to end. This is what
`content/en/cloud/guides/self-hosted/white-labeling/_index.md` (the
"Recipients therefore stay on your domain rather than being sent to the
canonical Layer5 Cloud host" bullet) already promises for footer links; it
is now also true of the verification link itself.
3. **Links sent before the fix** — a verification email delivered before the
release carrying meshery-cloud#6092 carries a link that cannot be completed
on a custom domain. Kratos flow links live 720h (30 days), so such links
remain in inboxes for up to a month after the release.
**Remedy: request a fresh verification email.** There is no way to repair an
already-sent link — the old link goes straight to the identity service and
no server hop can intercept it.

## Why this is filed rather than submitted as a PR

The meshery-cloud change was made in an isolated worktree whose rules forbid
modifying other checkouts, so the docs half could not ship in the same change
set. Flagging per meshery-cloud AGENTS.md §4 (external documentation in the
same PR) rather than leaving it unrecorded.

Start in content/en/cloud/getting-started/getting-started-with-layer5-account.md at §2, then read the custom-domain wording in content/en/cloud/guides/self-hosted/white-labeling/_index.md. Replace the circular reference with the email contents, custom-domain behavior, and remedy for links sent before the fix. Done means §2 contains complete verification guidance and the pre-release caveat.

Written by the indexing model from the issue text.