fix(dashboards): Hide prebuilt dashboards from All Dashboards list

Add excludePrebuilt filter to the dashboard list API call when viewing
All Dashboards. Prebuilt dashboards remain accessible via the Sentry
Built tab.

Refs LINEAR-DAIN-1415
Co-Authored-By: Claude Opus 4.6 <noreply@example.com>

Author: DominikB2014

static/app/views/dashboards/manage/index.tsx

@@ -208,7 +208,9 @@ function ManageDashboards() {
           pin: 'favorites',
           per_page:
             dashboardsLayout === GRID ? rowCount * columnCount : DASHBOARD_TABLE_NUM_ROWS,
-          ...(isOnlyPrebuilt ? {filter: DashboardFilter.ONLY_PREBUILT} : {}),
+          ...(isOnlyPrebuilt
+            ? {filter: DashboardFilter.ONLY_PREBUILT}
+            : {filter: DashboardFilter.EXCLUDE_PREBUILT}),
         },
       },
     ],