test(memory): cover pinned records in forgetting cycle

[77652189]

Summary

• Add regression coverage for pinned records during the memory forgetting cycle
• Verify pinned short-term records are not transitioned or included in generated summary sources

Testing

• corepack pnpm -C apps/web exec vitest run tests/unit/memory-forgetting.test.ts

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[Peefy]

Thank you! Good Job! LGTM!