Add test suite and fix configuration for Python 3.12

- Add AGENTS.md with coding guidelines for AI agents
- Add comprehensive unit tests for Binance adapter (mocked)
- Add integration tests for Binance testnet connectivity
- Fix pydantic-settings v2 compatibility for nested settings
- Fix MarginType enum to handle lowercase API responses
- Update Python requirement to 3.12+ (pandas-ta dependency)
- Update ruff config to new lint section format
- Update PLAN.md to reflect completed milestones 1.1-1.3

32 tests passing with 81% coverage

tests/test_config.py

@@ -1,6 +1,5 @@
 """Tests for configuration module."""
 
-import os
 from decimal import Decimal
 
 import pytest
@@ -101,7 +100,6 @@ class TestConfigValidation:
     def test_symbols_parsing_from_string(self) -> None:
         """Test comma-separated symbol parsing."""
         # This tests the validator logic directly
-        from tradefinder.core.config import Settings
 
         # Simulate what the validator does
         input_str = "BTCUSDT, ETHUSDT, SOLUSDT"
@@ -114,18 +112,43 @@ class TestConfigValidation:
         for tf in valid:
             # These should not raise
             assert tf in {
-                "1m", "3m", "5m", "15m", "30m", "1h", "2h", "4h",
-                "6h", "8h", "12h", "1d", "3d", "1w", "1M"
+                "1m",
+                "3m",
+                "5m",
+                "15m",
+                "30m",
+                "1h",
+                "2h",
+                "4h",
+                "6h",
+                "8h",
+                "12h",
+                "1d",
+                "3d",
+                "1w",
+                "1M",
             }
 
     def test_invalid_timeframe(self) -> None:
         """Test invalid timeframe is rejected."""
-        from tradefinder.core.config import Settings
 
         invalid_timeframes = ["2m", "10m", "2d", "1y", "invalid"]
         valid_set = {
-            "1m", "3m", "5m", "15m", "30m", "1h", "2h", "4h",
-            "6h", "8h", "12h", "1d", "3d", "1w", "1M"
+            "1m",
+            "3m",
+            "5m",
+            "15m",
+            "30m",
+            "1h",
+            "2h",
+            "4h",
+            "6h",
+            "8h",
+            "12h",
+            "1d",
+            "3d",
+            "1w",
+            "1M",
         }
         for tf in invalid_timeframes:
             assert tf not in valid_set