Bug: extremely long sources cause the Tags column to become extremely
wide. Caused by the source link not having the word-break property set.
Fix: use post_source_tag, which lets the `a[rel=external] { word-break: break-word; }`
rule take effect.
Example: https://danbooru.donmai.us/post_versions?search%5Bpost_id%5D=3809742