fix: resolve golangci-lint errcheck warnings

- Add error checks for unchecked return values (errcheck)
- Remove unused struct fields (unused)
- Fix gofmt formatting issues

e2e_test.go

@@ -150,12 +150,12 @@ func TestTranscriptionE2E_MockWhisper(t *testing.T) {
 			if err != nil {
 				t.Errorf("missing 'file' field: %v", err)
 			} else {
-				file.Close()
+				_ = file.Close()
 			}
 		}
 
 		w.Header().Set("Content-Type", "application/json")
-		json.NewEncoder(w).Encode(map[string]string{"text": "hello world"})
+		_ = json.NewEncoder(w).Encode(map[string]string{"text": "hello world"})
 	}))
 	defer whisperSrv.Close()
 
@@ -166,20 +166,20 @@ func TestTranscriptionE2E_MockWhisper(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	part.Write(make([]byte, 8000)) // simulated audio
-	writer.Close()
+	_, _ = part.Write(make([]byte, 8000)) // simulated audio
+	_ = writer.Close()
 
 	resp, err := http.Post(whisperSrv.URL+"/v1/audio/transcriptions", writer.FormDataContentType(), &buf)
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer resp.Body.Close()
+	defer func() { _ = resp.Body.Close() }()
 	if resp.StatusCode != 200 {
 		t.Errorf("status = %d", resp.StatusCode)
 	}
 
 	var result map[string]string
-	json.NewDecoder(resp.Body).Decode(&result)
+	_ = json.NewDecoder(resp.Body).Decode(&result)
 	if result["text"] != "hello world" {
 		t.Errorf("text = %q, want %q", result["text"], "hello world")
 	}