fix: WhatsApp @c.us Doppel-Suffix + Chat löschen in TUI

- WhatsApp send: @c.us wird vor dem Anhängen entfernt (verhindert 4915..@c.us@c.us)
- DELETE /api/v1/conversations/{id}: löscht Konversation + alle Nachrichten
- TUI: Taste D öffnet Bestätigungsdialog zum Löschen des aktuellen Chats

api/routes/conversations.py

@@ -1,4 +1,4 @@
-from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi import APIRouter, Depends, HTTPException, Query, status
 from sqlalchemy.orm import Session
 
 from api.auth import require_api_key
@@ -64,3 +64,15 @@ def get_messages(
     msgs = conversation_service.get_messages(db, conv_id, limit=limit, offset=offset)
     conversation_service.mark_all_read(db, conv_id)
     return [MessageResponse.model_validate(m) for m in msgs]
+
+
+@router.delete("/{conv_id}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_conversation(
+    conv_id: str,
+    db: Session = Depends(get_db),
+    _: str = Depends(require_api_key),
+):
+    conv = conversation_service.get_by_id(db, conv_id)
+    if not conv:
+        raise HTTPException(status_code=404, detail="Conversation not found")
+    conversation_service.delete(db, conv)