feat: Sprint 6 polish - methodology, demo data, deployment prep

- Add policy event markers to time series charts
- Create methodology page (/toronto/methodology) with data sources
- Add demo data module for testing without full pipeline
- Update README with project documentation
- Add health check endpoint (/health)
- Add database initialization script
- Export new figure factory functions

Closes #21

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

portfolio_app/pages/health.py

@@ -0,0 +1,20 @@
+"""Health check endpoint for deployment monitoring."""
+
+import dash
+from dash import html
+
+dash.register_page(
+    __name__,
+    path="/health",
+    title="Health Check",
+)
+
+
+def layout() -> html.Div:
+    """Return simple health check response."""
+    return html.Div(
+        [
+            html.Pre("status: ok"),
+        ],
+        id="health-check",
+    )