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/exceptions.py

@@ -0,0 +1,17 @@
+"""Custom exceptions for the portfolio application."""
+
+
+class PortfolioError(Exception):
+    """Base exception for all portfolio errors."""
+
+
+class ParseError(PortfolioError):
+    """PDF/CSV parsing failed."""
+
+
+class ValidationError(PortfolioError):
+    """Pydantic or business rule validation failed."""
+
+
+class LoadError(PortfolioError):
+    """Database load operation failed."""