Add complete Ouroboros trading system with TDD test suite

Implement the full autonomous trading agent architecture:
- KIS broker with async API, token refresh, leaky bucket rate limiter, and hash key signing
- Gemini-powered decision engine with JSON parsing and confidence threshold enforcement
- Risk manager with circuit breaker (-3% P&L) and fat finger protection (30% cap)
- Evolution engine for self-improving strategy generation via failure analysis
- 35 passing tests written TDD-first covering risk, broker, and brain modules
- CI/CD pipeline, Docker multi-stage build, and AI agent context docs

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

tests/conftest.py

@@ -0,0 +1,23 @@
+"""Shared test fixtures for The Ouroboros test suite."""
+
+from __future__ import annotations
+
+import pytest
+
+from src.config import Settings
+
+
+@pytest.fixture
+def settings() -> Settings:
+    """Return a Settings instance with safe test defaults."""
+    return Settings(
+        KIS_APP_KEY="test_app_key",
+        KIS_APP_SECRET="test_app_secret",
+        KIS_ACCOUNT_NO="12345678-01",
+        KIS_BASE_URL="https://openapivts.koreainvestment.com:9443",
+        GEMINI_API_KEY="test_gemini_key",
+        CIRCUIT_BREAKER_PCT=-3.0,
+        FAT_FINGER_PCT=30.0,
+        CONFIDENCE_THRESHOLD=80,
+        DB_PATH=":memory:",
+    )