feat: add token file and env Login

auth/config.go

@@ -0,0 +1,24 @@
+package auth
+
+const DefaultURL = "https://agent.robinhood.com/mcp/trading"
+const DefaultName = "robinhood-agentic-mcp"
+const DefaultVersion = "0.1.0"
+
+// Config is Login/Connect identity and the token file.
+type Config struct {
+	URL, TokenFile, Name, Version string
+}
+
+// WithDefaults fills empty URL, Name, and Version.
+func (c Config) WithDefaults() Config {
+	if c.URL == "" {
+		c.URL = DefaultURL
+	}
+	if c.Name == "" {
+		c.Name = DefaultName
+	}
+	if c.Version == "" {
+		c.Version = DefaultVersion
+	}
+	return c
+}