Refactor reverse proxy and enhance API routing

- Replaced the existing reverse proxy implementation with a new alias forwarding mechanism, improving path handling and request normalization.
- Updated the gateway to utilize the new forwarding approach, ensuring consistent handling of API requests and proper error management.
- Enhanced tests to validate the new routing behavior, including handling of double slashes and user endpoint requests.
- Improved documentation in GATEWAY_RUN.md to clarify the updated API routing and configuration requirements.

internal/proxy/join.go

@@ -0,0 +1,30 @@
+package proxy
+
+import (
+	"net/url"
+	"strings"
+)
+
+// JoinPathPrefix builds the upstream URL the same way as aggregate FetchTelemtGET:
+// base URL + path_prefix (e.g. /v1) + rest (e.g. health, stats/users) via url.JoinPath.
+func JoinPathPrefix(base *url.URL, pathPrefix, rest string) *url.URL {
+	rel := strings.Trim(pathPrefix, "/")
+	if rest != "" {
+		if rel != "" {
+			rel = rel + "/" + rest
+		} else {
+			rel = rest
+		}
+	}
+	var parts []string
+	for _, seg := range strings.Split(rel, "/") {
+		if seg != "" {
+			parts = append(parts, seg)
+		}
+	}
+	if len(parts) == 0 {
+		out := *base
+		return &out
+	}
+	return base.JoinPath(parts...)
+}