fix: legacy QR URLs without '?' (productid in path) redirect to /t/CODE (new tag 97 now scans); preview page photo portrait aspect; Preview button on user tags list; admin photo form = preview + standalone Upload button (removed URL TextInput — no duplicate, no stale placeholder)

frontend/main.go

@@ -70,7 +70,7 @@ func main() {
 	mux.HandleFunc("GET /about", app.About)
 	mux.HandleFunc("GET /what-is-this", app.WhatIsThis)
 	mux.HandleFunc("GET /contact", app.Contact)
-	mux.HandleFunc("/{path...}", http.NotFound)
+	mux.HandleFunc("/{path...}", app.LegacyNotFound)
 	mux.HandleFunc("GET /t/{tag_code}", app.PublicTag)
 	mux.HandleFunc("GET /s/{code}", app.ServeShort)
 	mux.HandleFunc("POST /t/{tag_code}/scan", app.Scan)