fix(lint): add return after t.Fatal to satisfy staticcheck SA5011

The staticcheck linter doesn't recognize that t.Fatal stops test
execution, so it warns about potential nil pointer dereference on
subsequent lines. Adding explicit return statements after t.Fatal
makes the control flow clear to the linter.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: technicalpickles

internal/cli/output/help_test.go

@@ -174,6 +174,7 @@ func TestExtractHelpInfo_Flags(t *testing.T) {
 
 	if outputFlag == nil {
 		t.Fatal("Expected to find 'output' flag")
+		return // unreachable but satisfies staticcheck SA5011
 	}
 
 	if outputFlag.Shorthand != "o" {

internal/config/merge_test.go

@@ -47,6 +47,7 @@ func TestMergeServerConfig_ScalarFieldReplacement(t *testing.T) {
 	// Verify diff captured changes
 	if diff == nil {
 		t.Fatal("Expected diff to be generated")
+		return // unreachable but satisfies staticcheck SA5011
 	}
 	if _, ok := diff.Modified["url"]; !ok {
 		t.Error("URL change not captured in diff")
@@ -322,6 +323,7 @@ func TestMergeServerConfig_ExplicitNullRemovesField(t *testing.T) {
 	// Verify diff captures removal
 	if diff == nil {
 		t.Fatal("Expected diff to be generated")
+		return // unreachable but satisfies staticcheck SA5011
 	}
 	found := false
 	for _, field := range diff.Removed {