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/pages/toronto/callbacks/chart_callbacks.py

@@ -5,7 +5,7 @@ import pandas as pd
 import plotly.graph_objects as go
 from dash import Input, Output, callback
 
-from portfolio_app.figures import (
+from portfolio_app.figures.toronto import (
     create_donut_chart,
     create_horizontal_bar,
     create_radar_figure,

portfolio_app/pages/toronto/callbacks/map_callbacks.py

@@ -4,7 +4,7 @@
 import plotly.graph_objects as go
 from dash import Input, Output, State, callback, no_update
 
-from portfolio_app.figures import create_choropleth_figure, create_ranking_bar
+from portfolio_app.figures.toronto import create_choropleth_figure, create_ranking_bar
 from portfolio_app.toronto.services import (
     get_amenities_data,
     get_demographics_data,