feat(dm): implement signed direct messaging with web push fallback

shine-server-db/src/main/java/shine/db/dao/SignedDirectMessagesHistoryDAO.java

@@ -0,0 +1,47 @@
+package shine.db.dao;
+
+import shine.db.SqliteDbController;
+import shine.db.entities.SignedDirectMessageHistoryEntry;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+
+public final class SignedDirectMessagesHistoryDAO {
+    private static volatile SignedDirectMessagesHistoryDAO instance;
+    private final SqliteDbController db = SqliteDbController.getInstance();
+
+    private SignedDirectMessagesHistoryDAO() {}
+
+    public static SignedDirectMessagesHistoryDAO getInstance() {
+        if (instance == null) {
+            synchronized (SignedDirectMessagesHistoryDAO.class) {
+                if (instance == null) instance = new SignedDirectMessagesHistoryDAO();
+            }
+        }
+        return instance;
+    }
+
+    public void insert(SignedDirectMessageHistoryEntry e) throws Exception {
+        try (Connection c = db.getConnection()) {
+            String sql = """
+                INSERT INTO signed_direct_messages_history (
+                    message_id, from_login, to_login, target_mode, target_session_id,
+                    message_type, time_ms, nonce, raw_packet, created_at_ms
+                ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+                """;
+            try (PreparedStatement ps = c.prepareStatement(sql)) {
+                ps.setString(1, e.getMessageId());
+                ps.setString(2, e.getFromLogin());
+                ps.setString(3, e.getToLogin());
+                ps.setInt(4, e.getTargetMode());
+                ps.setString(5, e.getTargetSessionId());
+                ps.setInt(6, e.getMessageType());
+                ps.setLong(7, e.getTimeMs());
+                ps.setLong(8, e.getNonce());
+                ps.setBytes(9, e.getRawPacket());
+                ps.setLong(10, e.getCreatedAtMs());
+                ps.executeUpdate();
+            }
+        }
+    }
+}