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>

src/strategies/base.py

@@ -0,0 +1,19 @@
+"""Base class for all trading strategies."""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Any
+
+
+class BaseStrategy(ABC):
+    """All strategies must inherit from this class."""
+
+    @abstractmethod
+    def evaluate(self, market_data: dict[str, Any]) -> dict[str, Any]:
+        """Evaluate market data and return a trade decision.
+
+        Returns:
+            dict with keys: action ("BUY"|"SELL"|"HOLD"), confidence (int), rationale (str)
+        """
+        ...