Unify topic folder routing and add manual INBOX re-sort trigger

[Copilot]

Emails from the same topic could be split across near-duplicate folders when AI returned slight naming variants. Users also needed a way to re-run sorting after a cycle had already finished.

• Folder normalization to prevent semantic duplicates

  • Extended AiClassificationService.NormalizeFolderName to resolve AI folder outputs against existing folders using a comparable key (case-insensitive, separator/punctuation-insensitive, accent-insensitive).
  • If exactly one existing folder matches the normalized key, that folder is reused instead of creating a new one.

• Manual re-sort entry point in UI

  • Added Korrekturen → INBOX erneut sortieren in MainForm.
  • Action reuses existing “mark INBOX unread” behavior and wakes the worker immediately so users can trigger correction runs on demand, even after prior processing completed.

• Focused behavior coverage

  • Added a classification test proving AI output variants (e.g. IT Entwicklung) map back to an existing folder (e.g. IT & Entwicklung) rather than creating a new folder.

var uniqueComparableMatch = TryFindUniqueComparableFolder(candidate, availableFolders);
if (!string.IsNullOrWhiteSpace(uniqueComparableMatch))
{
    return uniqueComparableMatch;
}