feat: Alpaca US stock trader integration (Tasks 8-11)

- trader/alpaca/: Full Trader interface implementation for Alpaca
  - Paper/Live trading support (market orders, stop/limit)
  - GetBalance, GetPositions, GetMarketPrice via Alpaca API
  - Fractional share support (4 decimal places)
  - Commission-free trading

- Agent trade routing: stock symbols (AAPL, TSLA) → Alpaca
  - isStockSymbol() heuristic to distinguish crypto vs stock
  - execute_trade tool updated for stock buy/sell semantics
  - get_market_price works for both crypto and stocks

- TraderManager + API: Alpaca registered as exchange type
  - Factory case in auto_trader.go
  - Config mapping in trader_manager.go
  - Temp trader creation in handler_trader.go for balance query

- Frontend: PositionsPanel distinguishes stock vs crypto
  - US flag emoji for stock positions
  - Dollar prefix for stock PnL/prices
  - 'Shares' label instead of 'Qty' for stocks

- System prompts updated for stock trading capabilities

agent/agent.go

@@ -475,10 +475,10 @@ func (a *Agent) buildSystemPrompt(lang string) string {
 ## 工具使用
 你可以调用以下工具来执行操作：
 - **search_stock** — 搜索股票（支持中文名、英文名、代码）。当用户提到你不认识的股票时，先用这个工具搜索。
-- **execute_trade** — 下单交易（做多/做空/平多/平空）。调用后会创建待确认订单，用户需回复"确认 trade_xxx"才会真正执行。
-- **get_positions** — 查看当前所有持仓
+- **execute_trade** — 下单交易（加密货币或美股）。美股：open_long=买入，close_long=卖出。调用后创建待确认订单，用户需回复"确认 trade_xxx"。
+- **get_positions** — 查看当前所有持仓（加密货币 + 股票）
 - **get_balance** — 查看账户余额
-- **get_market_price** — 获取交易所实时价格
+- **get_market_price** — 获取实时价格（加密货币或股票代码）
 
 ### 交易安全规则
 - 用户明确要求交易时才调用 execute_trade
@@ -536,10 +536,10 @@ func (a *Agent) buildSystemPrompt(lang string) string {
 ## Tools
 You can call these tools to take action:
 - **search_stock** — Search for stocks by name, ticker, or code. Covers A-share, HK, and US markets. Use when the user mentions an unknown stock.
-- **execute_trade** — Place a trade order (open_long/open_short/close_long/close_short). Creates a pending order that requires user confirmation.
-- **get_positions** — View all current open positions
+- **execute_trade** — Place a trade order (crypto or US stocks). For stocks: open_long=buy, close_long=sell. Creates a pending order that requires user confirmation.
+- **get_positions** — View all current open positions (crypto + stocks)
 - **get_balance** — View account balance and equity
-- **get_market_price** — Get real-time price from the exchange
+- **get_market_price** — Get real-time price from the exchange (crypto or stock symbol)
 
 ### Trade Safety Rules
 - Only call execute_trade when user explicitly requests a trade

agent/tools.go

@@ -40,7 +40,7 @@ func buildAgentTools() []mcp.Tool {
 			Type: "function",
 			Function: mcp.FunctionDef{
 				Name:        "execute_trade",
-				Description: "Execute a trade order. Use this when the user explicitly asks to open/close a position. This will create a pending trade that requires user confirmation before execution.",
+				Description: "Execute a trade order (crypto or US stocks). Use this when the user explicitly asks to open/close a position. For stocks (e.g. AAPL, TSLA), use open_long to buy and close_long to sell. This creates a pending trade that requires user confirmation.",
 				Parameters: map[string]any{
 					"type": "object",
 					"properties": map[string]any{
@@ -51,7 +51,7 @@ func buildAgentTools() []mcp.Tool {
 						},
 						"symbol": map[string]any{
 							"type":        "string",
-							"description": "Trading symbol, e.g. BTCUSDT, ETHUSDT. Always append USDT if not present.",
+							"description": "Trading symbol. For crypto: BTCUSDT, ETHUSDT. For US stocks: AAPL, TSLA, NVDA (no suffix needed).",
 						},
 						"quantity": map[string]any{
 							"type":        "number",
@@ -86,13 +86,13 @@ func buildAgentTools() []mcp.Tool {
 			Type: "function",
 			Function: mcp.FunctionDef{
 				Name:        "get_market_price",
-				Description: "Get the current market price for a symbol from the trader's exchange.",
+				Description: "Get the current market price for a crypto or stock symbol.",
 				Parameters: map[string]any{
 					"type": "object",
 					"properties": map[string]any{
 						"symbol": map[string]any{
 							"type":        "string",
-							"description": "Trading symbol, e.g. BTCUSDT",
+							"description": "Trading symbol, e.g. BTCUSDT for crypto, AAPL for stocks",
 						},
 					},
 					"required": []string{"symbol"},
@@ -205,7 +205,8 @@ func (a *Agent) toolExecuteTrade(_ context.Context, userID int64, lang, argsJSON
 
 	// Normalize symbol
 	sym := strings.ToUpper(args.Symbol)
-	if !strings.HasSuffix(sym, "USDT") {
+	// Only append USDT for crypto symbols; stock tickers (e.g. AAPL, TSLA) stay as-is
+	if !isStockSymbol(sym) && !strings.HasSuffix(sym, "USDT") {
 		sym += "USDT"
 	}
 
@@ -330,7 +331,7 @@ func (a *Agent) toolGetMarketPrice(argsJSON string) string {
 	}
 
 	sym := strings.ToUpper(args.Symbol)
-	if !strings.HasSuffix(sym, "USDT") {
+	if !isStockSymbol(sym) && !strings.HasSuffix(sym, "USDT") {
 		sym += "USDT"
 	}
 
@@ -459,3 +460,31 @@ func (a *Agent) toolGetTradeHistory(argsJSON string) string {
 	})
 	return string(result)
 }
+
+// isStockSymbol heuristically determines if a symbol is a stock ticker (not crypto).
+// Stock tickers are 1-5 uppercase letters without numeric suffixes like "USDT".
+// Known crypto suffixes: USDT, BTC, ETH, BNB, USDC, BUSD.
+func isStockSymbol(sym string) bool {
+	sym = strings.ToUpper(sym)
+	// If it already has a crypto quote suffix, it's crypto
+	cryptoSuffixes := []string{"USDT", "BUSD", "USDC", "BTC", "ETH", "BNB"}
+	for _, suffix := range cryptoSuffixes {
+		if strings.HasSuffix(sym, suffix) && len(sym) > len(suffix) {
+			return false
+		}
+	}
+	// Pure uppercase letters, 1-5 chars = likely a stock ticker
+	if len(sym) >= 1 && len(sym) <= 5 {
+		allLetters := true
+		for _, c := range sym {
+			if c < 'A' || c > 'Z' {
+				allLetters = false
+				break
+			}
+		}
+		if allLetters {
+			return true
+		}
+	}
+	return false
+}

agent/trade.go

@@ -153,6 +153,9 @@ func (a *Agent) executeTrade(ctx context.Context, trade *TradeAction) error {
 		return fmt.Errorf("no traders configured")
 	}
 
+	// Determine if this is a stock trade to route to the right exchange
+	wantStock := isStockSymbol(trade.Symbol)
+
 	// Find a running trader's underlying exchange interface
 	var underlyingTrader interface {
 		OpenLong(symbol string, quantity float64, leverage int) (map[string]interface{}, error)
@@ -169,12 +172,24 @@ func (a *Agent) executeTrade(ctx context.Context, trade *TradeAction) error {
 			if ut == nil {
 				continue
 			}
+			// Route stock symbols to alpaca traders, crypto to others
+			exchange := t.GetExchange()
+			isAlpaca := exchange == "alpaca"
+			if wantStock && !isAlpaca {
+				continue // Skip non-stock traders for stock symbols
+			}
+			if !wantStock && isAlpaca {
+				continue // Skip stock traders for crypto symbols
+			}
 			underlyingTrader = ut
 			break
 		}
 	}
 
 	if underlyingTrader == nil {
+		if wantStock {
+			return fmt.Errorf("no running stock trader (Alpaca) found — configure one to trade stocks")
+		}
 		return fmt.Errorf("no running trader supports trade execution")
 	}