feat: project bootstrap and structure

Sprint 1 initialization:
- Project directory structure (portfolio_app/, tests/, dbt/, data/, scripts/)
- CLAUDE.md with AI assistant context
- pyproject.toml with all dependencies
- docker-compose.yml for PostgreSQL 16 + PostGIS
- Makefile with standard targets
- Pre-commit configuration (ruff, mypy)
- Environment template (.env.example)
- Error handling foundation (PortfolioError hierarchy)
- Test configuration (conftest.py, pytest config)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,22 @@
+services:
+  db:
+    image: postgis/postgis:16-3.4
+    container_name: portfolio-db
+    restart: unless-stopped
+    ports:
+      - "5432:5432"
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER:-portfolio}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-portfolio_dev}
+      POSTGRES_DB: ${POSTGRES_DB:-portfolio}
+    volumes:
+      - postgres_data:/var/lib/postgresql/data
+      - ./scripts/db/init-postgis.sql:/docker-entrypoint-initdb.d/init-postgis.sql:ro
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-portfolio} -d ${POSTGRES_DB:-portfolio}"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
+
+volumes:
+  postgres_data: