i18n: add 11 more language catalogs; offer 10 in the selector

New translated catalogs (1929 strings each): Simplified Chinese, Traditional Chinese, Korean, Italian, Arabic, Hindi, Indonesian, Polish, Turkish, Vietnamese, Dutch.

Adds 10 of them to LANGUAGES (the selector now lists 17 languages). Arabic ships a complete catalog but is intentionally NOT offered yet: the UI needs right-to-left (bidi) layout work before it renders correctly, so enabling it now would look broken.

Same pipeline as the prior batch: a pinned per-language security glossary (severity levels, statuses, Finding/Vulnerability/etc.), every %s/%(name)s/{...} placeholder and HTML fragment preserved and verified token-by-token against English, distinct Simplified vs Traditional terms (e.g. zh-Hant 弱點/使用者). All catalogs pass 'msgfmt --check'; no fuzzy entries. DB values and serialized API responses remain English regardless of language.

These are machine-generated translations and would benefit from native-speaker review before being treated as authoritative.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: devGregA