feat: Add floating sidebar navigation and dark theme support

- Add floating pill-shaped sidebar with navigation icons
- Implement dark/light theme toggle with localStorage persistence
- Update all figure factories for transparent backgrounds
- Use carto-darkmatter map style for choropleths
- Add methodology link button to Toronto dashboard header
- Add back to dashboard button on methodology page
- Remove social links from home page (now in sidebar)
- Update CLAUDE.md to Sprint 7

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

portfolio_app/app.py

@@ -2,7 +2,9 @@
 
 import dash
 import dash_mantine_components as dmc
+from dash import dcc, html
 
+from .components import create_sidebar
 from .config import get_settings
 
 
@@ -17,14 +19,31 @@ def create_app() -> dash.Dash:
     )
 
     app.layout = dmc.MantineProvider(
-        dash.page_container,
+        id="mantine-provider",
+        children=[
+            dcc.Location(id="url", refresh=False),
+            dcc.Store(id="theme-store", storage_type="local", data="dark"),
+            dcc.Store(id="theme-init-dummy"),  # Dummy store for theme init callback
+            html.Div(
+                [
+                    create_sidebar(),
+                    html.Div(
+                        dash.page_container,
+                        className="page-content-wrapper",
+                    ),
+                ],
+            ),
+        ],
         theme={
             "primaryColor": "blue",
             "fontFamily": "'Inter', sans-serif",
         },
-        forceColorScheme="light",
+        defaultColorScheme="dark",
     )
 
+    # Import callbacks to register them
+    from . import callbacks  # noqa: F401
+
     return app