With base '' the built index.html references assets relatively
(./assets/*). On deep links like /listings/listing/:id the browser
resolves those below the route path, the SPA fallback answers with
index.html and the page dies trying to execute HTML as a JS module.
Notification emails link directly to listing details, so every
'Open in fredy' link landed on a white screen.
The web UI encodes the 'no swap flats' filter as exclusioncriteria=swapflat,
but the mobile API only accepts swap_flat. Unknown values are not ignored by
the API - the whole search silently returns 0 results, so any saved search
with this filter never finds a single listing.
Map the value during web-to-mobile conversion and leave all other
exclusioncriteria values (e.g. projectlisting, which both APIs share)
untouched.
The UI is served through a HashRouter, and most adapters (telegram,
slack, discord, ntfy, ...) already link to ${baseUrl}/#/listings/listing/:id.
The email adapters (resend, smtp, mailJet, sendGrid) and the http adapter
were missing the /# - the router never saw the route and dumped the user
on the default overview instead of the listing.
