Improve Docker image tagging strategy and remove Swagger version

- Replace 'stable' tag with semver-based tags (1.2.3, 1.2, 1)
- Use 'edge' tag for main branch instead of 'latest'
- Reserve 'latest' tag only for tagged releases
- Remove version from Swagger docs (tracked via git tags instead)
- Document available image tags in README

docs/docs.go

@@ -1208,7 +1208,7 @@ const docTemplate = `{
 
 // SwaggerInfo holds exported Swagger Info so clients can modify it
 var SwaggerInfo = &swag.Spec{
-	Version:          "1.0",
+	Version:          "",
 	Host:             "",
 	BasePath:         "/api/v1",
 	Schemes:          []string{},