Complete Korean (한국어) translations

[Copilot]

Korean translations were largely incomplete — only 4 locale files existed, several with untranslated English strings remaining.

Changes

New Korean locale files (23 files)

Covers all previously untranslated features:

• Auth/UX: devise.ko.yml, simple_form.ko.yml, profiles.ko.yml
• Course management: courses.ko.yml, school.ko.yml, admin.ko.yml
• Assessments: assignment.ko.yml, rubric.ko.yml, rubric_row_feedback.ko.yml, critique.ko.yml, submissions.ko.yml, installments.ko.yml
• Bingo/terms: candidates.ko.yml, candidate_results.ko.yml, concept.ko.yml
• Projects/experiences: projects.ko.yml, experiences.ko.yml, graphing.ko.yml
• Misc: ko.yml, activerecord.ko.yml, consent_logs.ko.yml, diagnosis.ko.yml, lti.ko.yml

Updated existing Korean files

• home.ko.yml — added calc_diversity_hdr, calc_diversity_instr, found_users, perspective_score, home.terms_lists.*; fixed typo 추소 → 취소
• intro.ko.yml — translated all remaining English strings (tooltips, section titles, slide captions, image alt text)

English file sync

• bingo_games.en.yml — added keys already present in the Korean file but missing from English: no_help_title, no_help_description, results.*, game_save_success, unable_to_save, demo_done, review_error