fix(lint): satisfy errcheck for io.Copy, json.Encode, Body.Close, deferred Close

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/skills/brain/handlers_test.go

@@ -18,7 +18,7 @@ func TestHandle_BrainQuery_CallsIngestServer(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		assert.Equal(t, "/query", r.URL.Path)
 		called = true
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"results": []map[string]any{
 				{"path": "wiki/concepts/tdd.md", "title": "TDD", "excerpt": "Test-driven development.", "score": 3},
 			},