FIX: improve Korean translations

[juunini]

Summary

• Correct Korean translations whose meanings were unrelated to the source text.
• Fix remaining English text, typos, and mistranslated 3D-printing terminology.
• Normalize terms such as seam, bed, wipe, and firmware retraction.
• Translate meaningful empty entries while preserving units, symbols, shortcuts, and product names.
• Preserve all source msgid/msgctxt values and runtime placeholders.

Validation

• msgfmt --check --check-format --statistics -o /dev/null bbl/i18n/ko/BambuStudio_ko.po
• git diff --check
• Custom placeholder parity check

Validation result: 5,619 translated messages, 32 intentionally untranslated unit/symbol/shortcut entries, with no format or placeholder errors.