feat: reset endpoint now liquidates Alpaca positions and cancels orders

- Added cancel_all_orders() and close_all_positions() to AlpacaBrokerAdapter
- Reset endpoint creates a temporary adapter to call Alpaca DELETE /v2/orders
  and DELETE /v2/positions before clearing DB and engine state
- Also clears positions table and processed_recommendation_ids on reset
- Broker reset is best-effort — DB/engine reset proceeds even if Alpaca fails

services/adapters/broker_adapter.py

@@ -276,6 +276,14 @@ class BrokerDataAdapter(BaseAdapter, ABC):
         """Get account summary (balance, buying power, etc.)."""
         ...
 
+    async def cancel_all_orders(self) -> int:
+        """Cancel all open orders. Returns the number of orders cancelled."""
+        return 0
+
+    async def close_all_positions(self) -> int:
+        """Liquidate all open positions. Returns the number of positions closed."""
+        return 0
+
 
 # --- Concrete Alpaca implementation ---
 
@@ -551,6 +559,50 @@ class AlpacaBrokerAdapter(BrokerDataAdapter):
                     mode=self._mode,
                 )
 
+    async def cancel_all_orders(self) -> int:
+        """Cancel all open orders on Alpaca.
+
+        Uses DELETE /v2/orders which cancels all open orders in bulk.
+        Returns the number of orders that were cancelled.
+        """
+        async with httpx.AsyncClient(timeout=30) as client:
+            try:
+                resp = await client.delete(
+                    f"{self.base_url}/v2/orders",
+                    headers=self._headers(),
+                )
+                resp.raise_for_status()
+                # Alpaca returns a list of cancelled order objects (HTTP 207)
+                data = resp.json()
+                cancelled = len(data) if isinstance(data, list) else 0
+                logger.info("Cancelled %d open orders on Alpaca", cancelled)
+                return cancelled
+            except Exception as e:
+                logger.error("Cancel all orders failed: %s", e)
+                return 0
+
+    async def close_all_positions(self) -> int:
+        """Liquidate all open positions on Alpaca.
+
+        Uses DELETE /v2/positions which closes all positions at market.
+        Returns the number of positions that were closed.
+        """
+        async with httpx.AsyncClient(timeout=30) as client:
+            try:
+                resp = await client.delete(
+                    f"{self.base_url}/v2/positions",
+                    headers=self._headers(),
+                )
+                resp.raise_for_status()
+                # Alpaca returns a list of closed position order objects (HTTP 207)
+                data = resp.json()
+                closed = len(data) if isinstance(data, list) else 0
+                logger.info("Closed %d positions on Alpaca", closed)
+                return closed
+            except Exception as e:
+                logger.error("Close all positions failed: %s", e)
+                return 0
+
     def _parse_order_response(self, data: dict[str, Any]) -> OrderResponse:
         """Parse an Alpaca order response into an OrderResponse."""
         status_map: dict[str, OrderStatus] = {