fix(webapp): use redirectWithErrorMessage for project-not-found in runs loader

Match the convention used by every other dashboard route (batches,
sessions, schedules): redirect to "/" with a toast on missing project,
rather than rendering a bare 404. The environment-not-found branch
remains a 404 via throwNotFound, since all peer routes for that case
were previously broken (bare Error → 500) and are now consistent.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: d-cs

apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs._index/route.tsx

@@ -40,6 +40,7 @@ import { useOrganization } from "~/hooks/useOrganizations";
 import { useProject } from "~/hooks/useProject";
 import { useSearchParams } from "~/hooks/useSearchParam";
 import { useShortcutKeys } from "~/hooks/useShortcutKeys";
+import { redirectWithErrorMessage } from "~/models/message.server";
 import { findProjectBySlug } from "~/models/project.server";
 import { findEnvironmentBySlug } from "~/models/runtimeEnvironment.server";
 import { getRunFiltersFromRequest } from "~/presenters/RunFilters.server";
@@ -78,7 +79,7 @@ export const loader = async ({ request, params }: LoaderFunctionArgs) => {
 
   const project = await findProjectBySlug(organizationSlug, projectParam, userId);
   if (!project) {
-    throwNotFound("Project not found");
+    return redirectWithErrorMessage("/", request, "Project not found");
   }
 
   const environment = await findEnvironmentBySlug(project.id, envParam, userId);