chore(i18n): regenerate translation catalogs with wp i18n tooling (#128)

Regenerate mail-system.pot with wp i18n make-pot and sync bg_BG/de_DE
with wp i18n update-po instead of hand-editing, so source references
carry exact file:line numbers and entries follow source order. Stale
strings no longer present in the code were dropped; strings that were
missing from the catalogs were added as untranslated entries. No
existing translation was changed or removed. MO files recompiled with
wp i18n make-mo.

Co-authored-by: Kilo <kilo@kilo.ai>

Author: katsar0v

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Themed API Reference documentation page** — the developer API reference is now published as a styled GitHub Pages subpage (`docs/api-reference.html`) that matches the project landing page, with a sticky "On this page" table of contents, syntax-highlighted PHP samples, copy-to-clipboard buttons on every code block, and a responsive layout. The Documentation links now open the rendered page instead of the raw Markdown file.
 
 ### Changed
+- **Translation catalogs regenerated with WP-CLI tooling** — `mail-system.pot`, `bg_BG.po` and `de_DE.po` are now produced by `wp i18n make-pot` / `wp i18n update-po` instead of hand edits, so source references carry exact file and line numbers and entries follow source order. Strings no longer present in the code were dropped from the catalogs; previously missing strings (e.g. database-repair notices) were added as untranslated entries so they are visible to translators. No translated string was changed or removed, and the `.mo` files are recompiled.
 
 ### Fixed
 - **Bulgarian status labels no longer mix singular and plural** — the campaign queue showed a single campaign as "Завършена" (feminine singular) next to "Отменени" (plural), because one string served both the status badge of a single item and the filter links that count many. Status, type and subscriber labels that describe a single row now use context-qualified strings (`_x()`), so Bulgarian can render campaign badges as feminine singular ("Завършена", "Отменена", "Насрочена"), email badges as masculine singular ("Изпратен", "Неуспешен", "Отменен") and the filter links as plural ("Завършени", "Отменени", "Насрочени"). German keeps its existing wording, and the date columns "Sent"/"Opened"/"Scheduled" now read as column headers ("Изпратен на", "Gesendet am") instead of as filter labels.