feat(auth): implement OAuth 2.0 authorization code flow and dynamic client registration

- Add OAuth 2.0 support with authorization code flow and dynamic client registration.
- Introduce new handlers for OAuth metadata, client registration, authorization, and token issuance.
- Enhance authentication middleware to support OAuth client credentials.
- Create in-memory stores for authorization codes and tokens.
- Update configuration to include OAuth client details.
- Ensure validation checks for OAuth clients in the configuration.

internal/config/loader.go

@@ -32,8 +32,10 @@ func Load(explicitPath string) (*Config, string, error) {
 }
 
 func ResolvePath(explicitPath string) string {
-	if strings.TrimSpace(explicitPath) != "" {
-		return explicitPath
+	if path := strings.TrimSpace(explicitPath); path != "" {
+		if path != ".yaml" && path != ".yml" {
+			return path
+		}
 	}
 
 	if envPath := strings.TrimSpace(os.Getenv("AMCS_CONFIG")); envPath != "" {
@@ -59,7 +61,6 @@ func defaultConfig() Config {
 			Transport:  "streamable_http",
 		},
 		Auth: AuthConfig{
-			Mode:       "api_keys",
 			HeaderName: "x-brain-key",
 			QueryParam: "key",
 		},