feat: heatmap metric toggle for both PP and TC views (Task B.4)

- Add Heatmap tab to Patient Pathways TAB_DEFINITIONS (was only in ALL_TAB_DEFINITIONS)
- Add dmc.SegmentedControl (Patients/Cost/Cost p.a.) to PP chart card header, hidden by default
- update_chart callback controls toggle visibility via heatmap-metric-wrapper style output
- _render_heatmap() now accepts metric param from toggle
- Add dmc.SegmentedControl to TC heatmap chart cell inline
- tc_heatmap callback reads tc-heatmap-metric-toggle value and passes metric to figure fn

dash_app/components/chart_card.py

@@ -1,11 +1,13 @@
 """Chart card component — tab bar, header, and dcc.Graph for charts."""
 from dash import html, dcc
+import dash_mantine_components as dmc
 
 
-# Patient Pathways view: only Icicle + Sankey
+# Patient Pathways view: Icicle, Sankey, Heatmap
 TAB_DEFINITIONS = [
     ("icicle", "Icicle"),
     ("sankey", "Sankey"),
+    ("heatmap", "Heatmap"),
 ]
 
 # Full set retained for Trust Comparison dashboard (Phase 10.8)
@@ -69,6 +71,23 @@ def make_chart_card():
                             ),
                         ]
                     ),
+                    # Heatmap metric toggle — visible only when heatmap tab active
+                    html.Div(
+                        id="heatmap-metric-wrapper",
+                        style={"display": "none"},
+                        children=[
+                            dmc.SegmentedControl(
+                                id="heatmap-metric-toggle",
+                                data=[
+                                    {"value": "patients", "label": "Patients"},
+                                    {"value": "cost", "label": "Cost"},
+                                    {"value": "cost_pp_pa", "label": "Cost p.a."},
+                                ],
+                                value="patients",
+                                size="xs",
+                            ),
+                        ],
+                    ),
                 ],
             ),
             # Chart area with loading spinner