[Bug] GUI Dataset Type selector includes YOLO but Evaluator only supports COCO — causes silent mismatch

**Description:**

In `app.py`, the sidebar Dataset Type selector offers two options:
```python
st.selectbox(
"Type",
["COCO", "YOLO"], # line 43
key="dataset_type",
)
```

But in `tabs/evaluator.py`, only COCO is handled:
```python
if dataset_type.lower() == "coco":
# loads dataset
else:
st.warning(
"⚠️ Only COCO datasets are currently supported for evaluation."
)
```

**The bug:** A user selects YOLO from the sidebar Dataset Type dropdown, navigates to the Evaluator tab, and sees a warning saying YOLO is not supported. However the sidebar still shows YOLO as a valid selectable option with no indication it won't work in the Evaluator tab — this is misleading and confusing.

**Steps to Reproduce:**
1. Open the GUI
2. In the sidebar, select `YOLO` as Dataset Type
3. Navigate to the Evaluator tab
4. See the warning — YOLO is not supported

**Expected Behaviour:**
Either YOLO should be supported in the Evaluator tab, or the Dataset Type selector should dynamically disable or hide YOLO when the user is on the Evaluator tab.

**Affected Files:**
- `app.py` — line 43
- `tabs/evaluator.py` — lines 44-48

Assign these task to me @vinitjain2005