feat(explorer): add _render_party_axis_chart helper

explorer.py

@@ -203,6 +203,73 @@ def load_party_map(db_path: str) -> Dict[str, str]:
         return {}
 
 
+def _render_party_axis_chart(
+    party_scores: Dict[str, List[float]], comp_sel: int
+) -> None:
+    """Render a 1D horizontal Plotly scatter of party positions on SVD axis `comp_sel`.
+
+    Each party is plotted at its score on a single horizontal axis (y=0).
+    """
+    if not party_scores:
+        st.caption("_Partijdata niet beschikbaar voor deze as._")
+        return
+
+    axis_idx = comp_sel - 1  # 0-based index into the 50-dim vector
+    data: list[dict] = []
+    for party, vec in party_scores.items():
+        if axis_idx < len(vec):
+            data.append({"party": party, "score": vec[axis_idx]})
+
+    if not data:
+        st.caption("_Geen partijscores voor deze as._")
+        return
+
+    scores = [d["score"] for d in data]
+    parties = [d["party"] for d in data]
+    colours = [PARTY_COLOURS.get(p, "#9E9E9E") for p in parties]
+    hover = [f"{p}: {s:.3f}" for p, s in zip(parties, scores)]
+
+    fig = go.Figure()
+    # Baseline
+    x_min, x_max = min(scores) * 1.15, max(scores) * 1.15
+    fig.add_trace(
+        go.Scatter(
+            x=[x_min, x_max],
+            y=[0, 0],
+            mode="lines",
+            line={"color": "#cccccc", "width": 1},
+            hoverinfo="skip",
+            showlegend=False,
+        )
+    )
+    # Party markers
+    fig.add_trace(
+        go.Scatter(
+            x=scores,
+            y=[0] * len(scores),
+            mode="markers+text",
+            text=parties,
+            textposition="top center",
+            marker={"size": 12, "color": colours},
+            hovertext=hover,
+            hoverinfo="text",
+            showlegend=False,
+        )
+    )
+    fig.update_layout(
+        height=160,
+        margin={"l": 10, "r": 10, "t": 10, "b": 30},
+        xaxis={
+            "title": "← Negatieve pool  |  Positieve pool →",
+            "zeroline": True,
+            "zerolinecolor": "#aaaaaa",
+        },
+        yaxis={"visible": False, "range": [-1, 2]},
+        plot_bgcolor="white",
+    )
+    st.plotly_chart(fig, use_container_width=True)
+
+
 @st.cache_data(show_spinner="Moties laden…")
 def load_motions_df(db_path: str) -> pd.DataFrame:
     """Load the full motions table as a pandas DataFrame (read-only)."""