email round trip and pricing page rebrand

[hannahhoward]

1. On the Storacha-branded console, when I enter my email, I should receive a Storacha-branded validation email.
2. When I click to verify my email, I should be taken to a Storacha-branded validation page (on [staging.]up.web3.storage, because that's where it has to be for now).

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• Create new Postmark template & layout for Storacha
• Modify Capability to trigger use of new template
• Point template to validation page with param set for Storacha branding

[Peeja]

I removed the mention of the Storacha-branded pricing page, because we actually have that already; it's the post-email validation page that needs branding.