feat: Enhance invoice file backup procedure to include JSON snapshots

- Updated the stored procedure `fds__admin_backupAndClearInvoiceFile.sql` to back up not only the invoice file but also JSON snapshots of related data (invoices, items, details, service requests) to ensure consistency and traceability.
- Modified the table structure of `fds__invoice_file_backups` to accommodate new JSON columns for storing these snapshots.
- Added an ADR (0030) document to outline the decision and rationale behind these changes, emphasizing the importance of maintaining a consistent set of data alongside the backed-up file.

Fuchs/Docs/Concepts/admin-specialties.md

@@ -22,6 +22,14 @@ rest of the Administration menu (`fds_sys > 4`), and reachable both from the
 menu (Administration → Spezialfunktionen) and by opening the URL
 `/specialties` directly.
 
+The menu entry is deliberately hidden: it only appears when the Administration
+dropdown is opened with **Shift** held (Shift+click, or Shift+Enter/Space on
+the focused toggle); a plain open hides it again
+(`$fis.bindShiftOnlyMenuItems` in `fis_main_menu.js`, driven by the item's
+`lclass: 'shift-only'`). This keeps the maintenance actions out of casual
+reach without adding another authorization level — the item is still part of
+the menu array, so the `/specialties` deep link is unaffected.
+
 ## How it works
 
 - **Module load** follows the standard contract (see