refactor(auth): remove obsolete CONVERT_PASSWORDS env var

Legacy md5/argon2id hashes are now always upgraded to bcrypt on login, so
the CONVERT_PASSWORDS flag is no longer used. Drop it from env schema,
.env.example, the docker installer, and test mocks.

scripts/docker-install.sh

@@ -78,7 +78,7 @@ else
   [[ "$auth_secret" =~ ^[0-9a-f]{64}$ ]] || fail "Could not generate the authentication secret."
   env_tmp="$(mktemp "$DIR/.env.install.XXXXXX")"
   {
-    printf '%s\n' 'NODE_ENV=production' 'PORT=3002' 'NEXT_TELEMETRY_DISABLED=1' 'AUTH_TRUST_HOST=true' 'CONVERT_PASSWORDS=true'
+    printf '%s\n' 'NODE_ENV=production' 'PORT=3002' 'NEXT_TELEMETRY_DISABLED=1' 'AUTH_TRUST_HOST=true'
     printf "HOTEL_NAME='%s'\nAPP_URL='%s'\nAUTH_URL='%s'\n" "$hotel" "$public_url" "$public_url"
     printf "DATABASE_URL='%s'\nREDIS_URL='%s'\nAUTH_SECRET='%s'\n" "$database_url" "$redis_url" "$auth_secret"
     printf "IMAGER_URL='%s'\nIMAGING_UPSTREAM_URL='%s'\nBADGE_URL='/swf/c_images/album1584'\n" "$imager_url" "$imager_url"