feat: implement main pipeline orchestrator (#54)

Add Pipeline class that wires together all detection components and
manages the event flow from trade ingestion to alerting.

Key features:
- Lifecycle management (start/stop) with proper cleanup
- Component initialization from Settings
- Parallel detector execution for fresh wallet and size anomaly
- Risk scoring with alert threshold
- Multi-channel alert dispatch (Discord/Telegram)
- Dry-run mode for testing without sending alerts
- Async context manager support
- Comprehensive test coverage (19 tests)

Pipeline flow: WebSocket → Profiler → Detectors → Scorer → Alerter

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

conftest.py

@@ -0,0 +1,14 @@
+"""Pytest configuration for the polymarket-insider-tracker tests."""
+
+import pytest
+
+# Configure pytest-asyncio
+pytest_plugins = ["pytest_asyncio"]
+
+
+@pytest.fixture(scope="session")
+def event_loop_policy():
+    """Use default event loop policy."""
+    import asyncio
+
+    return asyncio.DefaultEventLoopPolicy()