feat: add algo order compatibility and orphan order cleanup

- exchange.py: cancel_all_orders() now cancels both standard and algo orders
- exchange.py: get_open_orders() merges standard + algo orders
- exchange.py: cancel_order() falls back to algo cancel on failure
- bot.py: store SL/TP prices for price-based close_reason re-determination
- bot.py: add _cancel_remaining_orders() for orphan SL/TP cleanup
- bot.py: re-classify MANUAL close_reason as SL/TP via price comparison
- bot.py: cancel orphan orders on startup when no position exists
- tests: fix env setup for testnet config and ML filter mocking
- docs: add backtest market context and algo order fix design specs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_bot.py

@@ -19,6 +19,7 @@ def config():
         "NOTION_TOKEN": "secret_test",
         "NOTION_DATABASE_ID": "db_test",
         "DISCORD_WEBHOOK_URL": "",
+        "BINANCE_TESTNET": "false",
     })
     return Config()
 
@@ -34,6 +35,7 @@ def sample_df():
         "low":    close * 0.995,
         "close":  close,
         "volume": np.random.randint(100000, 1000000, n).astype(float),
+        "atr":    np.full(n, 0.005),
     })