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>

README.md

@@ -115,28 +115,31 @@ portfolio_app/
 │       ├── tabs/          # Tab layouts (5)
 │       └── callbacks/     # Interaction logic
 ├── components/            # Shared UI components
-├── figures/               # Plotly figure factories
+├── figures/
+│   └── toronto/           # Toronto figure factories
 ├── content/
 │   └── blog/              # Markdown blog articles
 ├── toronto/               # Toronto data logic
 │   ├── parsers/           # API data extraction
 │   ├── loaders/           # Database operations
 │   ├── schemas/           # Pydantic models
-│   └── models/            # SQLAlchemy ORM
+│   └── models/            # SQLAlchemy ORM (raw_toronto schema)
 └── errors/                # Exception handling
 
-dbt/
+dbt/                       # dbt project: portfolio
 ├── models/
-│   ├── staging/           # 1:1 source tables
-│   ├── intermediate/      # Business logic
-│   └── marts/             # Analytical tables
+│   ├── shared/            # Cross-domain dimensions
+│   ├── staging/toronto/   # Toronto staging models
+│   ├── intermediate/toronto/ # Toronto intermediate models
+│   └── marts/toronto/     # Toronto analytical tables
 
-notebooks/                 # Data documentation (15 notebooks)
-├── overview/              # Overview tab visualizations
-├── housing/               # Housing tab visualizations
-├── safety/                # Safety tab visualizations
-├── demographics/          # Demographics tab visualizations
-└── amenities/             # Amenities tab visualizations
+notebooks/
+└── toronto/               # Toronto documentation (15 notebooks)
+    ├── overview/          # Overview tab visualizations
+    ├── housing/           # Housing tab visualizations
+    ├── safety/            # Safety tab visualizations
+    ├── demographics/      # Demographics tab visualizations
+    └── amenities/         # Amenities tab visualizations
 
 docs/
 ├── PROJECT_REFERENCE.md   # Architecture reference