feat(07): add CSV format help text and Exchange 401 diagnostic hints

- CSV import dialog shows format line + example before mode selection
- Exchange connection test: on 401, inline hint lists common causes
  (wrong credentials, domain format, username prefix, O365 not supported)
- Both de/en translations updated

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -296,6 +296,8 @@
     "deleteVehicle": "Delete Vehicle",
     "deleteVehicleBody": "Vehicle {plate} will be permanently removed from the master list. This action cannot be undone.",
     "importCsv": "Import CSV",
+    "csvFormatHelp": "CSV format (semicolon): Kennzeichen;Marke;Modell;Fahrer",
+    "csvFormatExample": "Example: GP-JL 728E;Mercedes;GLC 300;Max Mustermann",
     "importMode": "Import Mode",
     "importMerge": "Merge — add new vehicles, keep existing",
     "importReplace": "Replace — delete all existing vehicles and re-import",
@@ -337,7 +339,12 @@
       "cancel": "Cancel Editing",
       "cancelDialog": "Cancel",
       "showPassword": "Show password",
-      "hidePassword": "Hide password"
+      "hidePassword": "Hide password",
+      "exchangeAuthHint": "401 — possible causes:",
+      "exchangeAuthHint1": "Wrong password or username",
+      "exchangeAuthHint2": "Domain: Windows short name (e.g. COMPANY, not company.com)",
+      "exchangeAuthHint3": "Username without domain prefix (e.g. 'max.muster', not 'COMPANY\\max.muster')",
+      "exchangeAuthHint4": "Office 365 / Exchange Online: EWS basic auth disabled since Oct 2022 — not supported"
     },
     "errors": {
       "pollFailed": "Could not check inbox. Review the configuration under 'Module Settings > Inbox'.",