fix: soften test-plan artifact assertion + increase CI timeout to 25min

The /plan-eng-review artifact test had a hard expect() despite the
comment calling it a "soft assertion." The agent doesn't always follow
artifact-writing instructions — log a warning instead of failing.

Also increase CI timeout 20→25min for plan tests that run full CEO
review sessions (6 concurrent tests, 276-315s each).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/evals.yml

@@ -63,7 +63,7 @@ jobs:
         username: ${{ github.actor }}
         password: ${{ secrets.GITHUB_TOKEN }}
       options: --user runner
-    timeout-minutes: 20
+    timeout-minutes: 25
     strategy:
       fail-fast: false
       matrix: