benchmark page: disclose the lifecycle vector row's pre-close statistics read (#17) - #18

Closes #17.

What changed

• export_web.py: a new October lifecycle sentence, vector_stats, printed under the lifecycle table when ArcadeDB's embedded dense-vector row is present. It says the row reads the index's statistics just before close, that the read is outside the timers, and that on this engine build it raises the close, so the row's open and close figure is an upper bound for a session that touches nothing. It carries no number, because the split is measured on the laptop only.
• CAMPAIGN.md section 7: row 22, moving the statistics read into one extra untimed cycle at the re-pin. The sentence retires with that row.

How it was verified

• _oct_conditions on a lifecycle table with the embedded vector row returns the new sentence beside the existing SurrealDB one; without that row it returns neither. The sentence has no digits, so it needs no page_check pin.
• The measurement behind it (laptop, 1M vectors, .notes/bench/repros/vector-clean-close/): clean close 6.4 ms without the read and 15.3 ms with it on de966e79c5; 3.0 and 3.5 ms on b8ab990821.
• October's lifecycle rows are not in the frozen CSV yet, so this changes no published payload until qOG lands; the landing's dry run will show the sentence.

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