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/PROJECT_REFERENCE.md

@@ -76,7 +76,8 @@ portfolio_app/
 ├── components/               # Shared UI components
 ├── content/blog/             # Markdown blog articles
 ├── errors/                   # Exception handling
-├── figures/                  # Plotly figure factories
+├── figures/
+│   └── toronto/              # Toronto figure factories
 ├── pages/
 │   ├── home.py
 │   ├── about.py
@@ -96,11 +97,21 @@ portfolio_app/
 │   ├── parsers/              # API extraction (geo, toronto_open_data, toronto_police, cmhc)
 │   ├── loaders/              # Database operations (base, cmhc, cmhc_crosswalk)
 │   ├── schemas/              # Pydantic models
-│   ├── models/               # SQLAlchemy ORM
+│   ├── models/               # SQLAlchemy ORM (raw_toronto schema)
 │   ├── services/             # Query functions (neighbourhood_service, geometry_service)
 │   └── demo_data.py          # Sample data
 └── utils/
     └── markdown_loader.py    # Blog article loading
+
+dbt/                          # dbt project: portfolio
+├── models/
+│   ├── shared/               # Cross-domain dimensions
+│   ├── staging/toronto/      # Toronto staging models
+│   ├── intermediate/toronto/ # Toronto intermediate models
+│   └── marts/toronto/        # Toronto mart tables
+
+notebooks/
+└── toronto/                  # Toronto documentation notebooks
 ```
 
 ---
@@ -144,10 +155,20 @@ CMHC Zones (~20) ← Rental data (Census Tract aligned)
 | `fact_rentals` | Fact | Rental data by CMHC zone |
 | `fact_amenities` | Fact | Amenity counts by neighbourhood |
 
-### dbt Layers
+### dbt Project: `portfolio`
+
+**Model Structure:**
+```
+dbt/models/
+├── shared/                 # Cross-domain dimensions (stg_dimensions__time)
+├── staging/toronto/        # Toronto staging models
+├── intermediate/toronto/   # Toronto intermediate models
+└── marts/toronto/          # Toronto mart tables
+```
 
 | Layer | Naming | Example |
 |-------|--------|---------|
+| Shared | `stg_dimensions__*` | `stg_dimensions__time` |
 | Staging | `stg_{source}__{entity}` | `stg_toronto__neighbourhoods` |
 | Intermediate | `int_{domain}__{transform}` | `int_neighbourhood__demographics` |
 | Marts | `mart_{domain}` | `mart_neighbourhood_overview` |