refactor: replace dmc.Drawer with dmc.Modal for filter selection (Task 7.4 + 7.5)

- Created 3 separate modals: Drug Selection (lg), Trust Selection (sm),
  Directorate Browser (xl) with centered overlay
- Added filter trigger buttons to filter bar with count badges
- Added "Clear All" button in filter bar for global filter reset
- Per-modal clear buttons for drugs and trusts
- Preserved all existing selection logic (same component IDs)
- Deleted drawer.py component and callbacks (replaced by modals.py)
- Updated CSS: filter-btn styles, modal chip/badge styles

dash_app/app.py

@@ -8,7 +8,7 @@ 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
-from dash_app.components.drawer import make_drawer
+from dash_app.components.modals import make_modals
 
 app = Dash(
     __name__,
@@ -34,7 +34,7 @@ app.layout = dmc.MantineProvider(
         # Page structure
         make_header(),
         make_sidebar(),
-        make_drawer(),
+        make_modals(),
         html.Main(
             className="main",
             children=[