Add cross-language translation status view

[lacatoire]

Summary

• Adds a new ?p=alllangs view on the EN revcheck page showing translation status across all languages as a color-coded matrix table
• Rows are files (from the EN tree), columns are translation languages, cells are colored by status (up to date, outdated, WIP, untranslated, etc.)
• Filterable by directory via a dropdown
• Adds an "All languages" link in the sidebar navigation when on the EN page

Test plan

• Visit revcheck.php?lang=en and verify the "View translation status across all languages" link appears
• Click the link and verify the directory dropdown and matrix table render correctly
• Change directory in the dropdown and verify the table updates
• Verify color coding matches the legend (green=up to date, red=outdated, orange=WIP, gray=untranslated, yellow=missing tag)
• Verify the "All languages" link appears in the sidebar on the EN page