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/js/intranet/fis_main_menu.js

@@ -17,7 +17,13 @@
    whose fds_sys authorization exceeds 4. One auth check gates the whole dropdown; it (and
    therefore all module scripts) is only added after that check resolves, so lower-privileged
    users never see it or fetch any module's code. Called from fis_main_go.js once the DOM (and
-   the initial main menu) is ready. Returns a promise that settles once the menu is final. */
+   the initial main menu) is ready. Returns a promise that settles once the menu is final.
+
+   Systemüberwachung and Spezialfunktionen are hidden entries: they are only shown while the
+   Administration dropdown is opened with the Shift key held (Shift+click on the toggle). A plain
+   click hides them again, so the diagnostics/maintenance pages are never one accidental click
+   away. The items still exist in the menu array, so the /admin and /specialties deep links
+   (openModuleFromPath) keep working. */
 $fis.addAdminMenuButtonsIfAuthorized = function () {
     if ($('#m_admin_grp').length > 0) { return Promise.resolve(); }   // idempotent
     return $fis.getAuth('fds_sys').then(function (auth) {
@@ -27,18 +33,32 @@ $fis.addAdminMenuButtonsIfAuthorized = function () {
                 itm: [
                     { lbl: $t.m_usr, id: 'm_usr', fnc: 'init:usr', ico: 'glyphicon glyphicon-user' },
                     { lbl: $t.m_usrgrp, id: 'm_usrgrp', fnc: 'init:usrgrp', ico: 'glyphicon glyphicon-list' },
-                    { lbl: $t.m_admin_status, id: 'm_admin', fnc: 'init:admin', ico: 'glyphicon glyphicon-dashboard' },
-                    { lbl: $t.m_specialties, id: 'm_specialties', fnc: 'init:specialties', ico: 'glyphicon glyphicon-wrench' }
+                    { lbl: $t.m_admin_status, id: 'm_admin', fnc: 'init:admin', ico: 'glyphicon glyphicon-dashboard', lclass: 'shift-only' },
+                    { lbl: $t.m_specialties, id: 'm_specialties', fnc: 'init:specialties', ico: 'glyphicon glyphicon-wrench', lclass: 'shift-only' }
                 ]
             });
             /* Re-render the main menu cleanly: drop the previously generated menu list
                (never the .nav-right settings dropdown) and rebuild it from the array. */
             $('#mainmenu').children('ul:not(.nav-right)').remove();
             $('#mainmenu').ocmsmenu($ocms.ocmsmenu);
+            $fis.bindShiftOnlyMenuItems($('#m_admin_grp'));
         }
     }).catch(function () { /* auth lookup failed → leave the menu unchanged */ });
 };
 
+/* Hides every `.shift-only` entry of a dropdown group and reveals them only for an opening
+   initiated with Shift held. Bound on mousedown (fires before Bootstrap's click toggle, so the
+   list is already in the right state when the dropdown becomes visible) and on keydown for
+   keyboard users (Shift+Enter / Shift+Space on the focused toggle). */
+$fis.bindShiftOnlyMenuItems = function (group) {
+    let items = group.find('.shift-only').hide();
+    if (items.length === 0) { return; }
+    let apply = function (e) { items.toggle(e.shiftKey === true); };
+    group.children('a.dropdown-toggle')
+        .on('mousedown', apply)
+        .on('keydown', function (e) { if (e.key === 'Enter' || e.key === ' ') { apply(e); } });
+};
+
 /* Deep link: the server renders the same SPA shell for every /{fn} URL (IntranetController.Index
    ignores fn), so opening e.g. /specialties directly would otherwise just show the dashboard.
    Opens the module named by the first path segment — but only one the user's menu actually