i18n(admin): translate the hardcoded text on 20 more admin screens

[ertugrulkeyvan]

What

A second round after #175: the remaining readable English on the admin screens now goes through translations.

HardcodedViewTextTest's ledger for the admin area goes from 132 to 110.

What is left is what should stay as written:

• example values, such as SUMMER20, mail.example.com, INBOX and spam@example.com;
• units and protocol names, such as KB, IMAP, POP3, SSL and STARTTLS;
• the Polish KSeF examples on the products page;
• fragments the detector reads from inline scripts and component attributes.

Translated, in three groups:

1. Back buttons and the quote's add-item button: clients, products, product groups, projects and quotes now use the existing common.actions.back and admin.invoices.add_item.

2. Detail pages:

   • the invoice, order, quote and SSL order titles, both the page title and the heading;
   • the invoice's "Paid on ";
   • the SSL order's service status.

   Invoice and order reuse admin.search.invoice_title and admin.search.order_title ("Invoice #:num", "Order #:num").

3. The rest:

   • the calendar's "+N more";
   • a project's "done/total tasks";
   • the report footer, "Showing N row(s) · Generated ";
   • the module log's action hint;
   • the custom field options hint;
   • the affiliate page heading;
   • the billable item amount label;
   • the logo's alt text in the admin header;
   • the addon page's "v… by …".

   The last four reuse existing keys: admin.billable_items.amount, admin.appearance.logo and admin.appearance.theme_by.

New keys: each is written in en, tr, de, pl and zh, with numbers, names and dates passed as placeholders, so each language orders them its own way.

How

• Commits: three, one per group above. Each holds the views, the new keys in the five language files, and the lower HardcodedViewTextTest ledger numbers.
• No behaviour changes: values, routes and form fields are untouched, and only text a person reads moved into __().

Tests

• HardcodedViewTextTest: passes with the lower ledger (admin 132 → 110).
• TranslationParityTest, DynamicTranslationParityTest, TranslationCoverageTest: pass. Every new key is in all five languages, no Turkish string keeps an English word, and no new key shadows an existing one.

Full suite: 4086 passed. The one failure is the CurrencyAndBackupTest db backup test, which fails on main too in my local setup.

[Panelica]

Thank you, @ertugrulkeyvan, merged. Twenty more admin screens now take their text from the translation files. Every key it uses gives the same English as the text it replaces, all five languages have the new entries in the same order, and the hardcoded-text budget went down with it.

Full suite green.