refactor: multi-dashboard structural migration

- Rename dbt project from toronto_housing to portfolio
- Restructure dbt models into domain subdirectories:
  - shared/ for cross-domain dimensions (dim_time)
  - staging/toronto/, intermediate/toronto/, marts/toronto/
- Update SQLAlchemy models for raw_toronto schema
- Add explicit cross-schema FK relationships for FactRentals
- Namespace figure factories under figures/toronto/
- Namespace notebooks under notebooks/toronto/
- Update Makefile with domain-specific targets and env loading
- Update all documentation for multi-dashboard structure

This enables adding new dashboard projects (e.g., /football, /energy)
without structural conflicts or naming collisions.

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

portfolio_app/components/metric_card.py

@@ -5,7 +5,7 @@ from typing import Any
 import dash_mantine_components as dmc
 from dash import dcc
 
-from portfolio_app.figures.summary_cards import create_metric_card_figure
+from portfolio_app.figures.toronto.summary_cards import create_metric_card_figure
 
 
 class MetricCard: