fix(monitor): 修正偏旁合体映射解析逻辑

问题：解析 unicode_radicals.md 时列索引错误，导致映射表为空

修复：
- 正确提取第5列（索引5）作为补充字符
- 修正 parts 数组索引：parts[4]=示例, parts[5]=补充字符

验证：
- 构建 45 条合体映射（如 '讠吾'→'语', '亻尔'→'你'）
- 测试还原：'默讠人'→'默认人', '亻尔'→'你'

monitor.py

@@ -102,16 +102,25 @@ def _load_radical_mapping() -> dict:
 
     返回: {OCR识别的偏旁组合: 正确汉字}
     例如: {'讠吾': '语', '亻牛': '件', '彳亍': '行'}
+
+    文件格式:
+    | 偏旁 | Unicode | 名称 | 示例 | 补充字符 |
+    |------|---------|------|------|----------|
+    | 亻 | U+4EBB | 单人旁 | 件→亻牛 | 件 |
+                         ↑ 索引3      ↑ 索引4
     """
     radical_map = {}
     try:
         with open(_RADICALS_MD, "r", encoding="utf-8") as f:
             for line in f:
-                if line.startswith("|") and "→" in line:
-                    parts = line.split("|")
-                    if len(parts) >= 5:
-                        example = parts[3].strip()  # 示例列: 件→亻牛
-                        corrected = parts[4].strip()  # 补充字符列: 件
+                if not line.startswith("|"):
+                    continue
+                parts = [p.strip() for p in line.strip().split("|")]
+                # parts[0] = 空, parts[1] = 偏旁, parts[2] = Unicode,
+                # parts[3] = 名称, parts[4] = 示例, parts[5] = 补充字符
+                if len(parts) >= 6 and "→" in parts[4]:
+                    example = parts[4]
+                    corrected = parts[5] if parts[5] else ""
                     if "→" in example and corrected:
                         ocr_form = example.split("→")[1].strip()
                         radical_map[ocr_form] = corrected