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/components/__init__.py

@@ -2,11 +2,13 @@
 
 from .map_controls import create_map_controls, create_metric_selector
 from .metric_card import MetricCard, create_metric_cards_row
+from .sidebar import create_sidebar
 from .time_slider import create_time_slider, create_year_selector
 
 __all__ = [
     "create_map_controls",
     "create_metric_selector",
+    "create_sidebar",
     "create_time_slider",
     "create_year_selector",
     "MetricCard",