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>

tests/__init__.py

@@ -0,0 +1 @@
+"""Test suite for analytics portfolio."""

tests/conftest.py

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+"""Pytest configuration and fixtures."""
+
+import pytest
+
+
+@pytest.fixture
+def sample_fixture():
+    """Example fixture - replace with actual fixtures as needed."""
+    return {}