feat: unify NofxOS data provider and fix language consistency

- Add unified NofxOS API key configuration in IndicatorEditor
- Add language field to StrategyConfig for consistent prompt generation
- Auto-update prompt sections when interface language changes
- Remove scattered URL inputs from CoinSourceEditor and IndicatorEditor
- Create nofxos provider package with formatted data output
- Update kernel engine to use config-based language setting

provider/nofxos/util.go

@@ -0,0 +1,31 @@
+package nofxos
+
+import "fmt"
+
+// Language represents the language for formatting output
+type Language string
+
+const (
+	LangChinese Language = "zh-CN"
+	LangEnglish Language = "en-US"
+)
+
+// formatValue formats a numeric value with sign and appropriate suffix
+func formatValue(v float64) string {
+	sign := "+"
+	if v < 0 {
+		sign = ""
+	}
+	absV := v
+	if absV < 0 {
+		absV = -absV
+	}
+	if absV >= 1e9 {
+		return fmt.Sprintf("%s%.2fB", sign, v/1e9)
+	} else if absV >= 1e6 {
+		return fmt.Sprintf("%s%.2fM", sign, v/1e6)
+	} else if absV >= 1e3 {
+		return fmt.Sprintf("%s%.2fK", sign, v/1e3)
+	}
+	return fmt.Sprintf("%s%.2f", sign, v)
+}