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>

portfolio_app/errors/__init__.py

@@ -0,0 +1,5 @@
+"""Error handling for the portfolio application."""
+
+from .exceptions import LoadError, ParseError, PortfolioError, ValidationError
+
+__all__ = ["PortfolioError", "ParseError", "ValidationError", "LoadError"]