- 🎨 Logó page in the CMS bottom bar: replace the website header logo and
the CMS login icon with a PNG upload (magic-byte validation, 1 MiB cap)
- the replaced logo gets a timestamped backup in .content-backups; every
upload is audited (logo_updated)
- /logo.png?variant=header serves the header variant for the preview
- publish stages proto/public too, so logo changes ride the same
commit+deploy pipeline as content
- route handling extracted to scripts/cms-logo.js to stay under the
400-line limit
- integration test: upload+replace+backup, variant preview, 415/413/400,
CSRF, auth
Closes MITHOME-65
