fix(decision): handle fullwidth JSON characters from AI responses

Extends fixMissingQuotes() to replace fullwidth brackets, colons, and commas that Claude AI occasionally outputs, preventing JSON parsing failures.
Root cause: AI can output fullwidth characters like ［｛：， instead of [{ :,
Error: "JSON 必须以 [{ 开头，实际: [ {"symbol": "BTCU"
Fix: Replace all fullwidth JSON syntax characters:
- ［］ (U+FF3B/FF3D) → []
- ｛｝ (U+FF5B/FF5D) → {}
- ： (U+FF1A) → :
- ， (U+FF0C) → ,
Test case:
Input:  ［｛\"symbol\"：\"BTCUSDT\"，\"action\"：\"open_short\"｝］
Output: [{\"symbol\":\"BTCUSDT\",\"action\":\"open_short\"}]
Co-Authored-By: tinkle-community <tinklefund@gmail.com>

decision/engine.go

@@ -459,12 +459,22 @@ func extractDecisions(response string) ([]Decision, error) {
 	return decisions, nil
 }
 
-// fixMissingQuotes 替换中文引号为英文引号（避免输入法自动转换）
+// fixMissingQuotes 替换中文引号和全角字符为英文引号和半角字符（避免AI输出全角JSON字符导致解析失败）
 func fixMissingQuotes(jsonStr string) string {
+	// 替换中文引号
 	jsonStr = strings.ReplaceAll(jsonStr, "\u201c", "\"") // "
 	jsonStr = strings.ReplaceAll(jsonStr, "\u201d", "\"") // "
 	jsonStr = strings.ReplaceAll(jsonStr, "\u2018", "'")  // '
 	jsonStr = strings.ReplaceAll(jsonStr, "\u2019", "'")  // '
+
+	// ⚠️ 替换全角括号、冒号、逗号（防止AI输出全角JSON字符）
+	jsonStr = strings.ReplaceAll(jsonStr, "［", "[") // U+FF3B 全角左方括号
+	jsonStr = strings.ReplaceAll(jsonStr, "］", "]") // U+FF3D 全角右方括号
+	jsonStr = strings.ReplaceAll(jsonStr, "｛", "{") // U+FF5B 全角左花括号
+	jsonStr = strings.ReplaceAll(jsonStr, "｝", "}") // U+FF5D 全角右花括号
+	jsonStr = strings.ReplaceAll(jsonStr, "：", ":") // U+FF1A 全角冒号
+	jsonStr = strings.ReplaceAll(jsonStr, "，", ",") // U+FF0C 全角逗号
+
 	return jsonStr
 }