fix(lint): resolve all errcheck violations in ingestion module

ingestion/internal/llm/client_test.go

@@ -18,7 +18,7 @@ func mockServer(t *testing.T, response string) *httptest.Server {
 		assert.Equal(t, "/chat/completions", r.URL.Path)
 		assert.Equal(t, "application/json", r.Header.Get("Content-Type"))
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"choices": []map[string]any{
 				{"message": map[string]any{"role": "assistant", "content": response}},
 			},
@@ -51,7 +51,7 @@ func TestClient_SendsAuthHeader(t *testing.T) {
 	var gotAuth string
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		gotAuth = r.Header.Get("Authorization")
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"choices": []map[string]any{{"message": map[string]any{"content": "ok"}}},
 		})
 	}))
@@ -72,7 +72,7 @@ func TestClient_Retries429(t *testing.T) {
 			w.WriteHeader(http.StatusTooManyRequests)
 			return
 		}
-		json.NewEncoder(w).Encode(map[string]any{
+		_ = json.NewEncoder(w).Encode(map[string]any{
 			"choices": []map[string]any{{"message": map[string]any{"content": "retried"}}},
 		})
 	}))