Adds paliad.countries (13 ISO-3166 codes), paliad.courts (41 entries
seeded from internal/handlers/courts.go), and the country/regime split
on paliad.holidays. The 33 t-paliad-121 UPC vacation rows previously
stored as country='UPC' migrate cleanly to country=NULL + regime='UPC'
— 'UPC' is a supranational regime, not an ISO country, and the new
shape lets a UPC LD München (country='DE', regime='UPC') pull both DE
federal holidays and UPC vacation entries while a UPC LD Paris
(country='FR', regime='UPC') pulls FR + UPC. Holidays now FK-protected
against typo'd country codes.
