Add version rollback support for AppImage updates

src/core/database.rs

@@ -1739,6 +1739,24 @@ impl Database {
         Ok(self.conn.last_insert_rowid())
     }
 
+    // --- Version rollback ---
+
+    pub fn set_previous_version(&self, id: i64, path: Option<&str>) -> SqlResult<()> {
+        self.conn.execute(
+            "UPDATE appimages SET previous_version_path = ?2 WHERE id = ?1",
+            params![id, path],
+        )?;
+        Ok(())
+    }
+
+    pub fn get_previous_version(&self, id: i64) -> SqlResult<Option<String>> {
+        self.conn.query_row(
+            "SELECT previous_version_path FROM appimages WHERE id = ?1",
+            params![id],
+            |row| row.get(0),
+        )
+    }
+
     // --- System modification tracking ---
 
     pub fn register_modification(