"Don't drink tea!"
Translation:Peidiwch ag yfed te!
No, the singular imperative of peidio is paid! and not peidia!, at least according to Gweiadur dictionary.
For some reason, Wiktionary gives the peidia! form, but I'm a bit suspicious.
The conjugation is auto-generated and perhaps whoever edited that entry didn't override the irregular form(s).
Yes, it'll be the auto-generated table.
Paid! is one of the phrases non-Welsh-speaking parents of Welsh-speaking kids learn very quickly!