refactor/fix: now using pgx errors for postgres error checking instead of trying to look up the error code;

feat: implemented working custom validation;
fix: authservice begin/complete registration

backend/go.mod

@@ -4,10 +4,10 @@ go 1.24.3
 
 require (
 	github.com/gin-gonic/gin v1.10.1
+	github.com/go-playground/validator/v10 v10.27.0
 	github.com/golang-jwt/jwt/v5 v5.2.2
 	github.com/jackc/pgx/v5 v5.7.5
 	github.com/spf13/viper v1.20.1
-	github.com/stretchr/testify v1.10.0
 	github.com/swaggo/files v1.0.1
 	github.com/swaggo/gin-swagger v1.6.0
 	github.com/swaggo/swag v1.16.4
@@ -20,7 +20,6 @@ require (
 	github.com/bytedance/sonic v1.13.3 // indirect
 	github.com/bytedance/sonic/loader v0.2.4 // indirect
 	github.com/cloudwego/base64x v0.1.5 // indirect
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
 	github.com/gabriel-vasile/mimetype v1.4.9 // indirect
 	github.com/gin-contrib/sse v1.1.0 // indirect
@@ -30,10 +29,8 @@ require (
 	github.com/go-openapi/swag v0.23.1 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
 	github.com/go-playground/universal-translator v0.18.1 // indirect
-	github.com/go-playground/validator/v10 v10.26.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
 	github.com/goccy/go-json v0.10.5 // indirect
-	github.com/jackc/pgerrcode v0.0.0-20240316143900-6e2875d9b438 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
 	github.com/jackc/puddle/v2 v2.2.2 // indirect
@@ -46,7 +43,6 @@ require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
-	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/sagikazarmark/locafero v0.9.0 // indirect
 	github.com/sourcegraph/conc v0.3.0 // indirect
 	github.com/spf13/afero v1.14.0 // indirect