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>

docs/CONTRIBUTING.md

@@ -290,7 +290,7 @@ Dashboard tabs are in `portfolio_app/pages/toronto/tabs/`.
 
 import dash_mantine_components as dmc
 
-from portfolio_app.figures.choropleth import create_choropleth
+from portfolio_app.figures.toronto.choropleth import create_choropleth
 from portfolio_app.toronto.demo_data import get_demo_data
 
 
@@ -339,13 +339,13 @@ dmc.TabsPanel(create_your_tab_layout(), value="your-tab"),
 
 ## Creating Figure Factories
 
-Figure factories are in `portfolio_app/figures/`. They create reusable Plotly figures.
+Figure factories are organized by dashboard domain under `portfolio_app/figures/{domain}/`.
 
 ### Pattern
 
 ```python
-# figures/your_chart.py
-"""Your chart type factory."""
+# figures/toronto/your_chart.py
+"""Your chart type factory for Toronto dashboard."""
 
 import plotly.express as px
 import plotly.graph_objects as go
@@ -382,7 +382,7 @@ def create_your_chart(
 ### Export from `__init__.py`
 
 ```python
-# figures/__init__.py
+# figures/toronto/__init__.py
 from .your_chart import create_your_chart
 
 __all__ = [
@@ -391,6 +391,14 @@ __all__ = [
 ]
 ```
 
+### Importing Figure Factories
+
+```python
+# In callbacks or tabs
+from portfolio_app.figures.toronto import create_choropleth_figure
+from portfolio_app.figures.toronto.bar_charts import create_ranking_bar
+```
+
 ---
 
 ## Branch Workflow