`fetchFromOpenverse` and `fetchFromWikimedia` were missing try/catch,
so a ConnectTimeoutError on `api.openverse.org` (frequent on networks
that can't reach Openverse) bubbled up to nitro's default handler and
turned a single image-search lookup into a HTTP 500 for the whole
design generation flow. The handler already treats `null` (Openverse)
and `[]` (Wikimedia) as the documented fallback signals — wrap the
fetches and return those on any throw, plus an explicit 8s
AbortSignal.timeout so the wait is bounded.
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