Scan manually added accounts

Manual accounts were never scanned:
- Sidebar "add user" entries had no platform, and getSelectedUsers()
  required platform === 'm365', so they were dropped from every scan.
- Profile-editor manual accounts were stored as "manual:<email>", which
  is not a Graph user id, and applying the profile never put them in the
  sidebar list, so they could not be selected.

Now the editor looks the email up via /api/users/lookup and stores the
directory id plus name/email (falling back to manual:<email> only when the
lookup fails). Applying a profile adds its manual accounts to the sidebar
and resolves legacy manual:<email> entries, logging any that can't be
found. The scan engine resolves remaining manual:<email> ids (e.g. from
scheduled scans) via the new M365Connector.lookup_user(), skipping and
reporting failures without widening to all users.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/de.json

@@ -534,6 +534,7 @@
   "m365_profile_applied": "Profil geladen",
   "m365_profile_acct_manual": "Manuell",
   "m365_profile_acct_unresolved": "Nicht geladen",
+  "m365_profile_manual_not_found": "Manuelles Konto in M365 nicht gefunden",
   "m365_profile_saved": "Profil gespeichert",
   "m365_profile_manage_btn": "Profile",
   "m365_profile_clear_btn": "Löschen",