next.config.ts has trailingSlash: true, so Next.js 308-redirects /icon to
/icon/. The middleware matcher only excluded the no-slash form, so after
the redirect the auth gate kicked in and bounced /icon/ to /cm-auth — the
browser got an HTML page where it expected a PNG, and the manifest icon
failed to install ('Download error or resource isn't a valid image').
- middleware: matcher now allows the optional slash on icon and apple-icon.
- manifest: point icons at the canonical /icon/ and /apple-icon/ URLs so
the browser fetches the PNG directly without a redirect round-trip.
