fix: restore correct behavior for --tools and --toolsets flags

Two behavioral regressions were fixed in resolveEnabledToolsets():

1. When --tools=X is used without --toolsets, the server should only
   register the specified tools, not the default toolsets. Now returns
   an empty slice instead of nil when EnabledTools is set.

2. When --toolsets=all --dynamic-toolsets is used, the 'all' and 'default'
   pseudo-toolsets should be removed so only the dynamic management tools
   are registered. This matches the original pre-refactor behavior.

Author: SamMorrowDrums

internal/ghmcp/server.go

@@ -123,13 +123,26 @@ func createGitHubClients(cfg MCPServerConfig, apiHost apiHost) (*githubClients,
 // resolveEnabledToolsets determines which toolsets should be enabled based on config.
 // Returns nil for "use defaults", empty slice for "none", or explicit list.
 func resolveEnabledToolsets(cfg MCPServerConfig) []string {
-	if cfg.EnabledToolsets != nil {
-		return cfg.EnabledToolsets
+	enabledToolsets := cfg.EnabledToolsets
+
+	// In dynamic mode, remove "all" and "default" since users enable toolsets on demand
+	if cfg.DynamicToolsets && enabledToolsets != nil {
+		enabledToolsets = github.RemoveToolset(enabledToolsets, string(github.ToolsetMetadataAll.ID))
+		enabledToolsets = github.RemoveToolset(enabledToolsets, string(github.ToolsetMetadataDefault.ID))
+	}
+
+	if enabledToolsets != nil {
+		return enabledToolsets
 	}
 	if cfg.DynamicToolsets {
 		// Dynamic mode with no toolsets specified: start empty so users enable on demand
 		return []string{}
 	}
+	if len(cfg.EnabledTools) > 0 {
+		// When specific tools are requested but no toolsets, don't use default toolsets
+		// This matches the original behavior: --tools=X alone registers only X
+		return []string{}
+	}
 	// nil means "use defaults" in WithToolsets
 	return nil
 }