✨ Redesign transactional mail and cover every account event

All mail now shares one monochrome layout (gray ground, hairline card, wordmark with the single emerald dot) built from inline-styled helpers in MailerHelper: eyebrow, heading, black or hairline button, one gray panel, mono block, status rows. Warnings are plain text with a bold lead-in, never a coloured box. Subjects drop their emoji. New mails, each hooked at the model or service so every entry point fires: - UserMailer#welcome on account creation, listing owned packages and the developer-mode extension install steps - ProjectMailer#created when an owned package is added (waitlist drafts skip) - DirectorySubmissionMailer#submissions_created when a maker queues directories, one row per directory with submit link and mode - WaitlistMailer#confirmation on a new waitlist signup - BillingMailer plan_activated / payment_failed / plan_cancelled from activate_plan!, grant_plan!, cancel_plan! and the Stripe webhook The unused batch_complete mail is removed. Previews for every variant live under test/mailers/previews with in-memory sample records, so /rails/mailers renders on an empty database. Adds mailer and hook tests, and a launch.json attach config for the dev server on :3109. :lipstick: Share one page header across public pages, replacing breadcrumbs Every public page (directories, guides, use cases, pricing, about, help, legal, extension, WebMCP) now opens with the same `shared/page_header` partial inside a `.page` frame, so the content edge and heading rhythm stop jumping between sections. The eyebrow links back to the section index with a dotted underline instead of a breadcrumb trail. Also: hand-drawn plan avatars on the pricing tiers, a grayscale footer logo that colours on hover, a base rule so every enabled button shows a pointer cursor, and the seed admin address moved to support@launchto.win.