feat: header fraction KPIs replacing KPI row (Task 10.3)

Remove KPI card row, add 3 inline fraction KPIs to header bar:
filtered/total patients, drugs, cost. Breadcrumb removed.
KPI callback refactored for 6 output IDs (3 filtered + 3 total).
total_cost added to load_initial_data() reference data.

dash_app/app.py

@@ -4,7 +4,6 @@ import dash_mantine_components as dmc
 
 from dash_app.components.header import make_header
 from dash_app.components.sidebar import make_sidebar
-from dash_app.components.kpi_row import make_kpi_row
 from dash_app.components.filter_bar import make_filter_bar
 from dash_app.components.chart_card import make_chart_card
 from dash_app.components.footer import make_footer
@@ -49,7 +48,6 @@ app.layout = dmc.MantineProvider(
                         html.Div(
                             id="patient-pathways-view",
                             children=[
-                                make_kpi_row(),
                                 make_filter_bar(),
                                 make_chart_card(),
                             ],