feat: HSM main/slave certificate comparison with batch SQL generation

- compare usercert_tab by subject raw bytes + certtype
- generate single annotated CSV report
- generate merge-<timestamp>.sql in current directory for DBA execution
- preserve GBK DN bytes via ATTACH + INSERT OR REPLACE / UPDATE
- compatible with sqlite3 3.6.20 and JDK 1.8

src/main/java/com/sunyard/certcompare/model/MergeChoice.java

@@ -0,0 +1,28 @@
+package com.sunyard.certcompare.model;
+
+/**
+ * 人工合并选择。报表中显示为“主”/“备”，内部使用枚举，SQL 中只出现 MAIN/SLAVE。
+ */
+public enum MergeChoice {
+    MAIN("主"),
+    SLAVE("备");
+
+    public final String label;
+
+    MergeChoice(String label) {
+        this.label = label;
+    }
+
+    public static MergeChoice fromText(String text) {
+        if (text == null) {
+            return null;
+        }
+        String t = text.trim();
+        for (MergeChoice c : values()) {
+            if (c.label.equals(t) || c.name().equalsIgnoreCase(t)) {
+                return c;
+            }
+        }
+        return null;
+    }
+}