Stored rankings version

Stored version for each OpenRouter rankings window in the digest. rankings_daily stores two windows. 2025-01-01 through 2025-12-31 stores v1. 2026-01-01 through 2026-10-27 stores v1. rankings_tool_calling and rankings_image_output store no windows, so they stay off this page. The label is the stored start date through the stored end date. The value is the stored version string. Both stored versions are v1, so the bars are equal. The bar is not a score. These versions are separate from the as-of time and from the file start and end dates. A window with no stored version stays off the page.