refactor routes,

use json encoding for route body parameters,
implement modify user/group/pool operations,
simplify schema by using comon lib struct tags and RequireAll and AtLeastOne helper functions,
properly implement locadb as Backend interface

app/localdb/utils.go

@@ -0,0 +1,19 @@
+package localdb
+
+import "reflect"
+
+// MergeNonZero overwrites fields in dst with fields in src iff src is not a zero value.
+func MergeNonZero[T any](dst *T, src *T) {
+	vDst := reflect.ValueOf(dst).Elem()
+	vSrc := reflect.ValueOf(src).Elem()
+
+	for i := 0; i < vDst.NumField(); i++ {
+		dstField := vDst.Field(i)
+		srcField := vSrc.Field(i)
+
+		// Only set if the field is exported (CanSet) and the source is not a zero value
+		if dstField.CanSet() && !srcField.IsZero() {
+			dstField.Set(srcField)
+		}
+	}
+}