Plotting additional metrics about authors

The [Author Directory](https://aclanthology.org/people/) has a nice plot of new authors per publication year, verified and unverified:

If they're not too difficult to make I would like to see 2 more plots on this page to help us understand the dynamics of authorship in our data:

1. Verification coverage by authorship: Number of namespecs that resolve to a verified vs. unverified person, by publication year.
2. Growth of our author database: Total verified and unverified authors in our database, measured every month starting Jan 2026.

The issue names no files or tests, so begin with the Author Directory page and locate the code that builds the existing per-year verified/unverified author plot. Trace the data source back to the author/year aggregation logic and namespec-to-person resolution, then extend it with the two requested metrics. Update the page template/renderer to surface both charts, and verify success by running the project’s normal build checks and checking the page output for correct year/month coverage and verified vs unverified series.

Written by the indexing model from the issue text.