Add the Hungarian catalog (4,524 rows): every menu string, every `tl!`
literal, the contextual and `@id` rows, the plurals and the status and
error messages, written from the meaning of the English labels in
general Hungarian vector-illustration vocabulary. Conventions are in the
header of `hu.tsv`.
- Register `hu` ("Magyar") in `i18n::LANGUAGES` as a complete language
with `plural_none` (a count takes the singular); every `hu-*` locale
resolves to it.
- Tests: Hungarian joins the menu-label, menu-string, `tl!`-literal and
message coverage checks; `hungarian_reads_as_hungarian` pins the core
vocabulary, the plural, the `file.close` override and a nested
message; ő ű Ő Ű are checked in the bundled UI fonts.
- README, ROADMAP, docs/development.md and docs/localization-parity.md
list Hungarian.
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