Replace the per-user CRUD-handler calls in seedDummyUsers with bulk
createMany inserts, plus several smaller wins on the seeding path.
End-to-end the preview create-project endpoint drops from ~15s to ~1.3s.

- seedDummyUsers: build every row up front and insert via one createMany
  per table inside a single transaction, instead of ~86 sequential
  adminCreate transactions. Named-user team memberships are bulk-inserted
  the same way. Idempotency is preserved via a single up-front email
  lookup, so re-runs against an existing project still skip existing
  users.
- Use node:crypto randomUUID instead of stack-shared generateUuid in the
  seed paths. The browser-safe polyfill calls crypto.getRandomValues ~31x
  per UUID, which dominated CPU time when generating thousands of seed
  UUIDs (~800ms in the activity-event build alone).
- seedBulkSignupsAndActivity: skip the redundant back-date UPDATE for
  freshly-inserted users (createMany already writes correct timestamps),
  and flush ClickHouse events in larger, parallel batches.
- seedDummyProject: run seedBulkSignupsAndActivity concurrently with the
  lighter remaining steps, and fold seedDummyTransactions into the
  emails/activity/replays Promise.all.
- Remove the now-unused syncSeedUserOauthProviders helper.

In preview mode the dashboard's /projects page renders PreviewProjectRedirect,
which POSTs /internal/preview/create-project and then router.push()es to
/projects/<new-id>. It never refreshed the client-side owned-projects cache,
so the [projectId] route's useAdminApp() read a stale list, failed to find the
just-created project, and called notFound() — showing a 404.

Refresh the owned-projects cache before navigating, matching what the normal
create-project flow in page-client.tsx already does.

LayoutClient's auto-login effect had no run-once guard. React StrictMode
(on by default in Next dev) double-invokes effects, and both invocations
ran while `user` was still null — so in preview mode each generated a
fresh `preview-*@Preview.stack-auth.com` email and signed up a *separate*
preview user.

With two users created per load, the session settles on one while the
preview project may have been created for the other, so the project page
renders a 404 ("does not have access to it").

Guard the effect with a ref so the auto-login (and preview-user creation)
runs at most once per mount.

…ve-conflicts-Z2kRC

# Conflicts:
#	apps/dashboard/src/app/(main)/(protected)/layout-client.tsx