fix: #5879 improve Italian translations - #5880

Closes #5879

Summary

Apply @topoldo’s Italian beta 2 translation from #5879, updating 153 strings across menus, commands, preferences, export settings and reading mode. The contribution improves Italian wording, terminology and punctuation, including clearer tab-navigation commands and the reading-mode label “Modalità a sola lettura”.

Correct the attachment’s missing JSON comma, a few spelling errors and the incomplete previous-tab command; preserve the meaning of overlapping folders and settings that apply to files opened subsequently. All 872 locale keys and interpolation placeholders match the English source. Translation credit is recorded in the commit’s Co-authored-by trailer.

Type of change

• Bug fix (non-breaking, fixes an issue)
• New feature (non-breaking, adds functionality)
• Breaking change (causes existing functionality to change)
• Documentation update

Test plan

• Existing locale-validation, i18n and context-menu locale suites: 81 tests passed. No new tests needed for this translation-only update.
• Italian reading-mode Electron E2E passed on macOS, checking the native menu, document-statistics popover, tab lock and text layout.
• pnpm run lint passed (0 errors; 166 existing warnings).
• pnpm run typecheck passed.
• pnpm run build:unpack passed.
• Prettier and JSON checks passed, including duplicate keys, key parity and placeholder preservation.
• Manually tested on: macOS (automated UI check completed; screenshot reviewed).

Screenshot

Italian reading-mode label and file-information heading on macOS:

Notes for reviewers

@topoldo’s review of the imported translation and proofreading adjustments is welcome.

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.