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/components/chart_card.py

@@ -1,19 +1,50 @@
-"""Chart card component — header and dcc.Graph for icicle chart."""
+"""Chart card component — tab bar, header, and dcc.Graph for charts."""
 from dash import html, dcc
 
 
+TAB_DEFINITIONS = [
+    ("icicle", "Icicle"),
+    ("market-share", "Market Share"),
+    ("cost-effectiveness", "Cost Effectiveness"),
+    ("cost-waterfall", "Cost Waterfall"),
+    ("sankey", "Sankey"),
+    ("dosing", "Dosing"),
+    ("heatmap", "Heatmap"),
+    ("duration", "Duration"),
+]
+
+
 def make_chart_card():
-    """Return a chart card matching 01_nhs_classic.html structure.
+    """Return a chart card with tab bar and dcc.Graph.
 
     Contains:
-    - Header with title and dynamic subtitle (hierarchy label)
+    - Tab bar with 8 chart tabs (Icicle active by default)
+    - Header with title and dynamic subtitle
     - dcc.Loading wrapper around dcc.Graph for loading spinner
-    Chart view selection (icicle/sankey/timeline) is in the sidebar.
     """
+    tab_buttons = []
+    for tab_id, label in TAB_DEFINITIONS:
+        is_active = tab_id == "icicle"
+        class_name = "chart-tab chart-tab--active" if is_active else "chart-tab"
+        tab_buttons.append(
+            html.Button(
+                label,
+                id=f"tab-{tab_id}",
+                className=class_name,
+                n_clicks=0,
+            )
+        )
+
     return html.Section(
         className="chart-card",
         **{"aria-label": "Patient pathway chart"},
         children=[
+            # Tab bar
+            html.Div(
+                className="chart-card__tabs",
+                role="tablist",
+                children=tab_buttons,
+            ),
             # Card header
             html.Div(
                 className="chart-card__header",

dash_app/components/sidebar.py

@@ -19,9 +19,6 @@ def _svg_icon(svg_body):
 # SVG icon bodies (Feather-style)
 _ICONS = {
     "pathway": '<rect x="3" y="3" width="7" height="7"/><rect x="14" y="3" width="7" height="7"/><rect x="14" y="14" width="7" height="7"/><rect x="3" y="14" width="7" height="7"/>',
-    "icicle": '<rect x="3" y="3" width="18" height="4" rx="1"/><rect x="3" y="10" width="10" height="4" rx="1"/><rect x="3" y="17" width="6" height="4" rx="1"/>',
-    "sankey": '<path d="M6 3v18"/><path d="M18 3v18"/><path d="M6 8c6 0 6 5 12 5"/><path d="M6 16c4 0 4-3 12-3"/>',
-    "timeline": '<line x1="3" y1="12" x2="21" y2="12"/><circle cx="6" cy="12" r="2"/><circle cx="12" cy="12" r="2"/><circle cx="18" cy="12" r="2"/>',
 }
 
 
@@ -39,16 +36,6 @@ def make_sidebar():
                     _sidebar_item("Pathway Overview", "pathway", active=True),
                 ],
             ),
-            # Chart views section
-            html.Div(
-                className="sidebar__section",
-                children=[
-                    html.Div("Chart Views", className="sidebar__label"),
-                    _sidebar_item("Icicle Chart", "icicle", active=True),
-                    _sidebar_item("Sankey Diagram", "sankey", disabled=True),
-                    _sidebar_item("Timeline", "timeline", disabled=True),
-                ],
-            ),
             # Footer
             html.Div(
                 className="sidebar__footer",
@@ -62,13 +49,11 @@ def make_sidebar():
     )
 
 
-def _sidebar_item(label, icon_key, active=False, disabled=False, item_id=None):
+def _sidebar_item(label, icon_key, active=False, item_id=None):
     """Create a single sidebar navigation item."""
     class_name = "sidebar__item"
     if active:
         class_name += " sidebar__item--active"
-    if disabled:
-        class_name += " sidebar__item--disabled"
 
     props = {"className": class_name}
     if item_id: