[bubulux]

Closes #14.

• Reverts Short page without the form until mails can be sent #13: the form, the notify route, its tests and the privacy sections are back.
• mail.ts: resendMailer posts to Resend's REST API with the key as bearer; mailerFor picks the injected test mailer, Resend with a key, a logging mailer locally without one, or a failing send. The send_email binding and the EMAIL env are gone; Ctx.mail carries the mailer.
• The Deploy workflow requires RESEND_API_KEY in the environment and sets it as a Worker secret after the deploy.
• The mail says "the OpenClapper alpha notification: one mail when the alpha starts", matching the page.
• The privacy page names Resend as the mail sender. docs/deploying.md has the Resend setup (domain, DNS, API key, the environment secret); architecture, development, forms and README updated.
• Tests: two new ones for the Resend request shape and error, and for the mailer choice. 21 route tests.

Checked locally: a sign-up logs the mail with its link; the link confirms and lands on /?confirmed=yes#waitlist.

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