fix(frontend): hide delete control on AutoGPT-managed credentials (#13085)

## Why

Deleting an "Ayrshare (managed by AutoGPT)" credential from `Settings →
Integrations` on dev fails with the toast "Failed to remove integration
... Try again to retry the failed ones." This isn't a transient failure
— the backend deliberately rejects deletes of `is_managed=True`
credentials with `HTTP 403 "AutoGPT-managed credentials cannot be
deleted"`
([router.py:518-522](https://github.com/Significant-Gravitas/AutoGPT/blob/dev/autogpt_platform/backend/backend/api/features/integrations/router.py#L518-L522)).
For Ayrshare specifically there's no upstream profile-delete API anyway,
and the managed-credentials sweep would just re-provision on the next
list call.

The frontend `CredentialRow` rendered the trash button + select checkbox
unconditionally, leading users to attempt an action the platform doesn't
support and get a generic error.

## What

- `CredentialRow`: hide the per-row select checkbox and trash button
when `credential.isManaged === true`; show a small "Managed" tag in
their place.
- `useIntegrationsList`: exclude managed credentials from the
`allCredentialIds` list that feeds "select all", so bulk-delete also
skips them.
- Add an integration test asserting both controls are absent for managed
credentials.

## How

The `isManaged` flag is already on `CredentialView` (mapped from backend
`is_managed`). The fix is purely a render-time gate plus a filter in the
select-all id collection; no API or store changes.

Note: linking/unlinking the individual social networks inside the
managed Ayrshare profile happens on the Ayrshare-hosted page reached via
`GET /ayrshare/sso_url` (already wired through the Connect flow in the
block UI) — not from this settings page.

## Checklist

- [x] Integration test covers the new behavior
- [x] `pnpm format` / `pnpm types` clean for changed files
- [x] No backend changes required