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

docs/PLAN.md

@@ -16,26 +16,26 @@ Automated crypto trading system for BTC/ETH perpetual futures with regime-adapti
 - [x] Docker configuration
 - [x] Environment template
 
-### Milestone 1.2: Configuration & Core
-- [ ] Pydantic settings with validation
-- [ ] Structured logging (structlog)
-- [ ] Error handling patterns
+### Milestone 1.2: Configuration & Core ✅
+- [x] Pydantic settings with validation
+- [x] Structured logging (structlog)
+- [x] Error handling patterns
 
-### Milestone 1.3: Exchange Adapter
-- [ ] Abstract exchange interface
-- [ ] Binance USDⓈ-M Futures adapter
-  - [ ] Hedge mode (dual position side)
-  - [ ] Isolated margin per symbol
-  - [ ] Leverage configuration
-  - [ ] Order types: limit, stop-market
-- [ ] Testnet connectivity verification
+### Milestone 1.3: Exchange Adapter ✅
+- [x] Abstract exchange interface
+- [x] Binance USDⓈ-M Futures adapter
+  - [x] Hedge mode (dual position side)
+  - [x] Isolated margin per symbol
+  - [x] Leverage configuration
+  - [x] Order types: limit, stop-market
+- [x] Testnet connectivity verification
 
 ### Milestone 1.4: Data Ingestion
-- [ ] REST OHLCV fetcher (historical backfill)
+- [x] REST OHLCV fetcher (historical via get_candles)
 - [ ] WebSocket streams (real-time)
   - [ ] Kline/candlestick
-  - [ ] Mark price
-  - [ ] Funding rate
+  - [ ] Mark price (REST available)
+  - [ ] Funding rate (REST available)
 - [ ] DuckDB storage schema
 - [ ] Data validation & gap detection