fix: Sankey freeform arrangement + increased padding (Task B.3)

IMPLEMENTATION_PLAN.md

@@ -109,9 +109,9 @@ Comprehensive review and improvement of all Plotly charts in the Dash dashboard.
 - **Checkpoint**: Lollipop dots show smooth green→amber→red gradient
 
 ### B.3 Sankey narrow-screen fix
-- [ ] In `create_sankey_figure()` (~L788):
-  - Change `arrangement="snap"` → `arrangement="freeform"`
-  - Increase `pad` from 20 → 25
+- [x] In `create_sankey_figure()` (~L808):
+  - Changed `arrangement="snap"` → `arrangement="freeform"`
+  - Increased `pad` from 20 → 25
 - **Checkpoint**: Sankey nodes don't overlap on narrow viewports
 
 ### B.4 Heatmap metric toggle (both views)

src/visualization/plotly_generator.py

@@ -805,9 +805,9 @@ def create_sankey_figure(
 
     fig = go.Figure(
         go.Sankey(
-            arrangement="snap",
+            arrangement="freeform",
             node=dict(
-                pad=20,
+                pad=25,
                 thickness=25,
                 line=dict(color="#FFFFFF", width=1),
                 label=node_labels,