feat(nofxi): K-line chart with TradingView lightweight-charts

- Candlestick chart + volume histogram
- 8 trading pairs: BTC/ETH/SOL/BNB/XRP/DOGE/ADA/AVAX
- 5 timeframes: 15m/1H/4H/1D/1W
- Real-time price & 24h change display
- Auto-refresh every 30s
- Backend: /api/klines + /api/ticker (Binance futures API)
- Dark trading terminal theme, responsive resize
- Tab switching: Chat ↔ Chart

nofxi/internal/interaction/kline.go

@@ -0,0 +1,126 @@
+package interaction
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strconv"
+	"time"
+)
+
+// KlineBar represents a single candlestick.
+type KlineBar struct {
+	Time   int64   `json:"time"`
+	Open   float64 `json:"open"`
+	High   float64 `json:"high"`
+	Low    float64 `json:"low"`
+	Close  float64 `json:"close"`
+	Volume float64 `json:"volume"`
+}
+
+// fetchKlines gets kline data from Binance public API (no auth needed).
+func fetchKlines(symbol, interval string, limit int) ([]KlineBar, error) {
+	if limit <= 0 {
+		limit = 200
+	}
+	url := fmt.Sprintf("https://fapi.binance.com/fapi/v1/klines?symbol=%s&interval=%s&limit=%d",
+		symbol, interval, limit)
+
+	client := &http.Client{Timeout: 10 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		return nil, fmt.Errorf("fetch klines: %w", err)
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	var raw [][]interface{}
+	if err := json.Unmarshal(body, &raw); err != nil {
+		return nil, fmt.Errorf("parse klines: %w", err)
+	}
+
+	bars := make([]KlineBar, 0, len(raw))
+	for _, k := range raw {
+		if len(k) < 6 {
+			continue
+		}
+		bar := KlineBar{
+			Time: int64(k[0].(float64)) / 1000, // ms → seconds for lightweight-charts
+		}
+		bar.Open, _ = strconv.ParseFloat(k[1].(string), 64)
+		bar.High, _ = strconv.ParseFloat(k[2].(string), 64)
+		bar.Low, _ = strconv.ParseFloat(k[3].(string), 64)
+		bar.Close, _ = strconv.ParseFloat(k[4].(string), 64)
+		bar.Volume, _ = strconv.ParseFloat(k[5].(string), 64)
+		bars = append(bars, bar)
+	}
+	return bars, nil
+}
+
+// RegisterKlineRoutes adds kline API endpoints to the mux.
+func RegisterKlineRoutes(mux *http.ServeMux) {
+	// GET /api/klines?symbol=BTCUSDT&interval=1h&limit=200
+	mux.HandleFunc("/api/klines", func(w http.ResponseWriter, r *http.Request) {
+		symbol := r.URL.Query().Get("symbol")
+		if symbol == "" {
+			symbol = "BTCUSDT"
+		}
+		interval := r.URL.Query().Get("interval")
+		if interval == "" {
+			interval = "1h"
+		}
+		limitStr := r.URL.Query().Get("limit")
+		limit := 200
+		if l, err := strconv.Atoi(limitStr); err == nil && l > 0 {
+			limit = l
+		}
+		if limit > 1000 {
+			limit = 1000
+		}
+
+		bars, err := fetchKlines(symbol, interval, limit)
+		if err != nil {
+			w.Header().Set("Content-Type", "application/json")
+			w.WriteHeader(http.StatusBadGateway)
+			json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
+			return
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		json.NewEncoder(w).Encode(bars)
+	})
+
+	// GET /api/ticker?symbol=BTCUSDT — current price + 24h change
+	mux.HandleFunc("/api/ticker", func(w http.ResponseWriter, r *http.Request) {
+		symbol := r.URL.Query().Get("symbol")
+		if symbol == "" {
+			symbol = "BTCUSDT"
+		}
+
+		url := fmt.Sprintf("https://fapi.binance.com/fapi/v1/ticker/24hr?symbol=%s", symbol)
+		client := &http.Client{Timeout: 10 * time.Second}
+		resp, err := client.Get(url)
+		if err != nil {
+			w.WriteHeader(http.StatusBadGateway)
+			json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
+			return
+		}
+		defer resp.Body.Close()
+
+		body, err := io.ReadAll(resp.Body)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		w.Header().Set("Access-Control-Allow-Origin", "*")
+		w.Write(body)
+	})
+}

nofxi/internal/interaction/web.go

@@ -140,6 +140,9 @@ func (w *WebServer) Start(ctx context.Context) error {
 		})
 	})
 
+	// Register kline/market data API
+	RegisterKlineRoutes(mux)
+
 	// Serve web UI static files
 	if w.webDir != "" {
 		if _, err := os.Stat(filepath.Join(w.webDir, "index.html")); err == nil {