Extract and apply StartupWMClass for proper taskbar icons

Parse StartupWMClass from embedded .desktop entries during analysis,
store in DB, include in generated .desktop files. Detail view shows
an editable WM class field with apply button for manual override.

src/core/database.rs

@@ -1754,6 +1754,14 @@ impl Database {
         Ok(())
     }
 
+    pub fn set_startup_wm_class(&self, id: i64, wm_class: Option<&str>) -> SqlResult<()> {
+        self.conn.execute(
+            "UPDATE appimages SET startup_wm_class = ?2 WHERE id = ?1",
+            params![id, wm_class],
+        )?;
+        Ok(())
+    }
+
     // --- Launch statistics ---
 
     pub fn get_top_launched(&self, limit: i32) -> SqlResult<Vec<(String, u64)>> {