i18n: add Korean (ko) UI localization — full catalog, glossary-checked

[riyenas0925]

Adds Korean as a selectable UI language. All 696 msgids in the current main catalog are translated (device UI, web UI, SQM/Bortle descriptions), terminology was checked against the Korean Astronomical Society glossary and against everyday Korean amateur-astronomy usage, and the result was verified on a headless PiFinder run.

Background

#500 started Korean support earlier this year but has not been merged, and the string set has moved on since then. Rather than rebase that draft, this PR builds a fresh catalog against today's main. The code side lands on the same approach as #500 (reuse the Sarasa CJK font, restart on language switch, --lang ko, menu entry), so there is no design disagreement — thanks to @hjoungjoo for the groundwork. Happy to coordinate if merging into #500 is preferred.

Translations — 696 entries, 0 untranslated

• Astronomical nouns follow the Korean Astronomical Society glossary (한국천문학회 천문학용어집): 산개성단, 구상성단, 행성상성운, 암흑성운, 이중성, 별자리, 황도광, 대일조, 대기광, 대암극, 성도, 초점거리, 구경, 극축 정렬.
• Operational jargon follows what Korean amateur astronomers actually say rather than forced native coinages: plate solving → 솔빙, align → 얼라인 (which also frees 정렬 for sort), eyepiece → 아이피스, mount → 마운트, seeing → 시잉, catalog → 카탈로그, DSO → 딥스카이, reticle → 레티클. EPOCH, Knot, N/A stay in English because no Korean term is in common use.
• EQ, Alt/Az, RA/Dec and GPS are kept verbatim per the i18n conventions.
• Named placeholders, leading spaces, embedded newlines and Nerd-Font keypad glyphs are preserved exactly; checked by script.
• Multi-line hints (polar align, software update, GPS) were re-split across lines to read naturally in Korean word order.
• Every entry carries the repo's # AI-TRANSLATED (claude): needs human review marker so reviewers can find and clear them. One low-confidence entry (Appeal → 매력도) is also marked #, fuzzy and falls back to English until reviewed.
• The other four catalogs only gain the two new msgids (Korean, Language: ko).

Code changes

• main.py, server.py: accept ko in the --lang validation list and the Flask accept_languages list.
• ui/menu_structure.py: Korean entry in Settings → Language, plus the Language: ko marker string.
• ui/fonts.py: zh and ko both use sarasa-mono-sc-light-nerd-font+patched.ttf (verified via fontTools that it carries the full Hangul range).
• ui/callbacks.py: restart after switching to ko, same as zh, since the font set changes.
• docs/source/menu_map.rst: Korean added to the Language values.

Verification

• pybabel compile --statistics: 696/696 for de, es, fr, ko, zh.
• Ran headless (--display headless, 128×128) with language: ko and walked main menu, Settings → Chart/Language/User Pref, Objects → By Catalog, Tools → Equipment, SQM. No missing glyphs, no truncation at base font size.
• ruff check on the five touched files; pytest -m smoke passes (web/Selenium tests skipped, no grid).

Not addressed here

• Switching from ko/zh back to a Latin language does not trigger a restart, so the CJK font stays loaded until the next boot. Pre-existing behaviour for zh; left as is.
• Korean glyphs are double-width, so a few long menu labels sit close to the right edge on the 128 px panel. Nothing clips at the sizes shipped, but the 176 px panel was not screenshot-checked.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WErqKyPNdq326xqryfMJLX