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>

notebooks/README.md

@@ -1,17 +1,18 @@
-# Toronto Neighbourhood Dashboard - Notebooks
+# Dashboard Documentation Notebooks
 
-Documentation notebooks for the Toronto Neighbourhood Dashboard visualizations. Each notebook documents how data is queried, transformed, and visualized using the figure factory pattern.
+Documentation notebooks organized by dashboard project. Each notebook documents how data is queried, transformed, and visualized using the figure factory pattern.
 
 ## Directory Structure
 
 ```
 notebooks/
 ├── README.md              # This file
-├── overview/              # Overview tab visualizations
-├── housing/               # Housing tab visualizations
-├── safety/                # Safety tab visualizations
-├── demographics/          # Demographics tab visualizations
-└── amenities/             # Amenities tab visualizations
+└── toronto/               # Toronto Neighbourhood Dashboard
+    ├── overview/          # Overview tab visualizations
+    ├── housing/           # Housing tab visualizations
+    ├── safety/            # Safety tab visualizations
+    ├── demographics/      # Demographics tab visualizations
+    └── amenities/         # Amenities tab visualizations
 ```
 
 ## Notebook Template