Replace the sample data with synthetic fixtures and regenerate goldens and thumbnails

The template harness, tests and thumbnails now use a neutral vendor, bank account and
a generated sample wordmark (scripts/logo/make-sample-logo.mjs). Layout goldens and the
14 picker thumbnails are regenerated. Fixture strings keep their original lengths where
layout tests depend on them.

src-tauri/src/integrations/erpnext/client.rs

@@ -404,7 +404,7 @@ mod tests {
             .await
             .unwrap();
         let raw = mock.requests.lock().unwrap()[0].clone();
-        assert!(raw.starts_with("GET /api/resource/Sales%20Invoice/AP%2F2026-001?limit_page_length=0 "), "{raw}");
+        assert!(raw.starts_with("GET /api/resource/Sales%20Invoice/INV%2F2026-001?limit_page_length=0 "), "{raw}");
     }
 
     #[tokio::test]