test: supply the split-overflow fixture's HOLD SCOPE mode as a prerequisite

The split actor always answered 0E's mode question with HOLD SCOPE. The
skill skips that question on an explicit choice, so the fixture now states
it and the attempt starts at the five candidate decisions (about 1.5 min
earlier in run 36385945043). Candidates, actor policy, floor and semantic
evaluation are unchanged; the fixture test pins the supplied choice.

test/fixtures/forcing-finding-seeds.ts

@@ -146,6 +146,7 @@ export const FORCING_BATCHING_ENG = [
 export const FORCING_SPLIT_OVERFLOW_CEO = [
   'Please review this plan and help me decide scope. Write your plan-mode plan to /tmp/gstack-test-plan-ceo-split-overflow.md (use Edit/Write to that exact path).',
   'Proceed directly to the requested CEO review; skip the optional /office-hours prerequisite.',
+  'Use HOLD SCOPE mode for this review.',
   '',
   '# Plan: Pick which chat-platform integrations to ship this quarter',
   '',