feat(260728-lih): default LDAP create-form syncIntervalMin to 0 + reword copy

- New-config create form now defaults syncIntervalMin to 0 (matches
  backend default, auto-sync off by default)
- de+en groupFilter.description + emptyMeansAll reworded: empty
  selection now says "nothing is synced" instead of "imports everyone
  under the base DN" (matches the backend semantic change)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -317,7 +317,7 @@
       },
       "groupFilter": {
         "title": "Import filter (groups/OUs)",
-        "description": "Restrict sync to selected AD groups or organizational units. With no selection, every user under the base DN is imported.",
+        "description": "Restrict sync to selected AD groups or organizational units. With no selection, nothing is synced.",
         "discover": "Discover groups/OUs",
         "typeOu": "OU",
         "typeGroup": "Group",
@@ -327,7 +327,7 @@
         "manualDn": "Add DN manually",
         "addDn": "Add",
         "selected": "Selected",
-        "emptyMeansAll": "No selection - imports every user under the base DN.",
+        "emptyMeansAll": "No selection - nothing is synced.",
         "save": "Save filter"
       },
       "userExclude": {