The Kobo store proxy feature was failing with 404 errors for certain
store endpoints (e.g., /v1/products/featuredforkoboplus/) because
Flask's routing couldn't match these paths. This prevented the Discover
tab from working when "Proxy unknown requests to Kobo Store" was enabled.
Added catch-all routes using Flask's path converter to match any
/v1/products/* paths not handled by more specific routes, allowing
the proxy logic to properly redirect these requests to the official
Kobo store API.
