feat: add parsing utilities and 8-tab chart infrastructure (Task 9.1)

- Create src/data_processing/parsing.py with parse_average_spacing(),
  parse_pathway_drugs(), and calculate_retention_rate()
- Add 8-tab bar to chart_card.py (Icicle, Market Share, Cost Effectiveness,
  Cost Waterfall, Sankey, Dosing, Heatmap, Duration)
- Add active-tab dcc.Store and tab switching callback in chart.py
- Remove Chart Views section from sidebar (now in tab bar)
- Lazy rendering: only active tab's chart is computed

dash_app/app.py

@@ -29,6 +29,7 @@ app.layout = dmc.MantineProvider(
         }),
         dcc.Store(id="chart-data", storage_type="memory"),
         dcc.Store(id="reference-data", storage_type="session"),
+        dcc.Store(id="active-tab", storage_type="memory", data="icicle"),
         dcc.Location(id="url", refresh=False),
 
         # Page structure