feat(relay): support configurable frps webui port and fix node detail integration

- Implement configurable FRPS WebUI switch and custom port setting (relay_frps_web_ui_port) in system configs.
- Integrate settings into Relay Node detail manage page instead of global settings.
- Dynamically query server version to select matching Docker image tag for Relay installation.
- Clean up legacy code and fix backend linter/test warnings.

internal/apps/openflare/agent/helpers.go

@@ -105,14 +105,6 @@ func applyNodeRuntime(ctx context.Context, node *model.OpenFlareNode, payload No
 	}
 }
 
-func cloneCoordinate(value *float64) *float64 {
-	if value == nil {
-		return nil
-	}
-	cloned := *value
-	return &cloned
-}
-
 func truncateForDatabase(value string, maxVal int) string {
 	if maxVal <= 0 {
 		return ""