feat(web): Verwaltung „Eigene Module“

- Liste, Anlegen, Bearbeiten und Löschen unter Verwaltung, Adresse wird im Formular geprüft
- Seitenleiste zieht nach jedem Speichern oder Löschen ohne Neuladen nach
- Texte deutsch und englisch, Eintrag in der Admin-Leiste hinter „Module“

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -85,6 +85,7 @@
       "users": "Users",
       "tenants": "Tenants",
       "modules": "Modules",
+      "customModules": "Custom modules",
       "ldap": "LDAP",
       "smtp": "SMTP",
       "groups": "Groups"
@@ -668,6 +669,29 @@
       "grants": {
         "matrixCheckboxLabel": "{granted, select, true {Grant} other {Revoke}} {module} for group {group}"
       }
+    },
+    "customModules": {
+      "title": "Custom modules",
+      "description": "Add other websites as entries in the sidebar. All users see these entries under the chosen category, and a click shows the page right inside Tessera.",
+      "create": "Add custom module",
+      "edit": "Edit custom module",
+      "name": "Name",
+      "url": "Address",
+      "urlHint": "The address must start with https://.",
+      "category": "Category",
+      "actions": "Actions",
+      "noModules": "No custom modules yet",
+      "noModulesBody": "Add your first module to show a website in the sidebar.",
+      "nameRequired": "Please enter a name.",
+      "urlNotHttps": "Please enter an address that starts with https://.",
+      "urlCredentials": "The address must not contain a user name or a password.",
+      "saveError": "The module could not be saved. Please try again.",
+      "deleteError": "The module could not be deleted. Please try again.",
+      "loadError": "The custom modules could not be loaded.",
+      "deleteConfirm": {
+        "title": "Delete custom module",
+        "body": "Do you really want to delete “{name}”? The entry disappears from the sidebar for all users."
+      }
     }
   },
   "adminModules": {