Logos resolve domain, then tenant, then server-wide, then the built-in, with
subdomains finding their domain. GET /logo serves a data-URL image, redirects
to a URL logo without fetching it, sandboxes SVG, and answers 404 when no
custom logo applies. Emails embed the first PNG, JPEG or GIF logo. Logo and
template writes are checked; stored templates are read at send time, always
escaped, and fall back to the built-in with a build warning when they don't
parse. The RSVP page is served byte for byte with a CSP and no-referrer. The
sign-in and RSVP pages load the logo through an image element. MT-22's
session logo follows the chain to the server-wide logo.
Acceptance tests 1 to 17; test 18 written as the ignored branding_compat.
Test 3 expects invalidForeignKey, as MT-3 says. A tenant admin reads its own
tenant through sysTenantGet and sysTenantQuery, added to the default Tenant
Administrator role for new installs only. The server adds nothing for MT-7's
dashboard list. The MT-19a submission warning is deferred. MT-22's logo is
the urn:inbuxa:jmap account capability's logo field (contract C-1).