headplot func w test runner

[ngup1]

-added modern headplot function following finns structure
-added runner test file to test generating plots

[madhuritha22]

The head-plot module and standalone script look solid and useful for export workflows.
However — I don’t see integration code that adds head-plots to the GUI’s graph viewer flow yet. As is, head-plots seem only accessible via the script runner, not via the in-app visualization.
Could you clarify whether GUI integration is planned for this sprint? If yes, please add wiring in GraphViewerScene (or equivalent) to call plot_head() when appropriate.
If not — let’s document clearly that head-plots are only available through the export script.

[Omanhene20]

Module Architecture - Integration Concern

I see the headplot function follows Finn's structure which is good for consistency.
However, I agree with @madhuritha22's concern about GUI integration.

Questions:

1. Is there a specific reason head plots are separated from the main GraphViewerScene workflow?
2. What's the technical barrier to adding it to the GUI alongside fin/tail plots?

Suggestion:
Consider creating a PlotRegistry or PlotFactory pattern that allows easy registration
of new plot types. This would make adding future plot types (spine plots, movement overlays)
more maintainable:

class PlotRegistry:
    _plotters = {}
    
    @classmethod
    def register(cls, name, plotter_func):
        cls._plotters[name] = plotter_func
    
    @classmethod
    def get_available_plots(cls):
        return list(cls._plotters.keys())

[Omanhene20]

Testing Coverage** ⭐

On the test runner file, add:

**Automated Testing - Test Coverage**

Good initiative adding a test runner! However, I have some concerns about test comprehensiveness:

**Current State:**
- ✅ Tests plot generation (good!)
- ❌ Missing edge case tests
- ❌ No validation of plot output correctness

**Recommended Test Cases:**
1. **Empty data**: What happens when the CSV has no valid frames?
2. **NaN values**: How does the plot handle missing head coordinates?
3. **Single frame**: Edge case with only 1 data point
4. **Invalid config**: Missing required fields in config JSON
5. **Output validation**: Check that generated plots have expected data ranges

**Example test structure:**
```python
def test_headplot_empty_data():
    """Test head plot handles empty DataFrame gracefully."""
    empty_df = pd.DataFrame()
    config = load_test_config()
    
    # Should either skip gracefully or raise informative error
    with pytest.raises(ValueError, match="No data to plot"):
        plot_head(empty_df, config)

def test_headplot_output_has_correct_traces():
    """Verify generated plot contains expected data."""
    df = load_test_data()
    config = load_test_config()
    
    fig = plot_head(df, config)
    assert len(fig.data) > 0  # Has trace data
    assert fig.layout.xaxis.title.text == "Time (s)"  # Correct axis labels

Adding these tests would prevent regressions and improve code reliability

[Omanhene20]

1. Is there a specific reason head plots are separated from the main GraphViewerScene workflow?