HN ranking and repost work expanded

Recent HN Trend Tracker changes concentrated on the work that makes a historical tracker more useful: dbt-backed all-time rankings, better recent-window ranking behavior on the homepage, and more deliberate handling of repost summaries.

This direction fits the project well. The app is strongest when it records score movement, repost recurrence, and ranking drift over time rather than trying to become a general-purpose news product.