Added dashboard for package activity

[javabster]

(This is a PR from PyCon US 2026 Sprint - was nice meeting you all!)

fixes #100

Summary

Adds a new dashboard page for tracking maintenance activity across pyOpenSci-accepted packages.

Changes

• New page: pyos-packages/package-activity.qmd
• New navbar entry: pyos-packages → Package Activity in _quarto.yml

The new page shows:

• A sortable table of all packages with name, description, last commit date, stars, forks, watchers, contributors, and open issues.
• A filtered table of packages with no commits in the last 6 months.

Data is read from _data/package_data.csv, which is already produced by the existing scripts/get-package-data.py cron

Open Questions

I wasn't sure if this data should be a whole new page or just included in the existing "accepted package metrics" page. Happy to change it if needed