Normalize `db_repos` to use short names in coverage dashboard

[rubambiza]

As noted in #17 (comment):

nit (pre-existing): db_repos keeps the full owner/repo form here, while lh_repos (line 355) and the new pr_repos (line 369) use split("/")[1] short names. In the cross-program coverage table this can produce a duplicate row for a repo covered by dep-bump plus another program (kagenti vs owner/kagenti).

This issue tracks the follow-up work to normalize db_repos to use short names (like lh_repos and pr_repos) after PR #17 is merged.

[rubambiza]

/claim

[rubambiza]

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