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

tui/screens/main_screen.py

@@ -25,6 +25,7 @@ class MainScreen(Screen):
         Binding("n", "new_message", "Neu"),
         Binding("r", "refresh", "Aktualisieren"),
         Binding("t", "telegram_qr", "Telegram QR"),
+        Binding("d", "delete_conv", "Chat löschen"),
         Binding("q", "quit_app", "Beenden"),
     ]
 
@@ -241,6 +242,35 @@ class MainScreen(Screen):
         if self._current_conv_id:
             await self._load_messages(self._current_conv_id)
 
+    def action_delete_conv(self) -> None:
+        if not self._current_conv_id:
+            self.notify("Kein Chat ausgewählt.", severity="warning")
+            return
+        title = (self._current_conv or {}).get("title") or self._current_conv_id[:8]
+        self.app.push_screen(
+            _ConfirmScreen(f"Chat löschen?\n\n{title}\n\nAlle Nachrichten werden entfernt."),
+            self._delete_conv_callback,
+        )
+
+    def _delete_conv_callback(self, confirmed: bool) -> None:
+        if confirmed:
+            asyncio.create_task(self._do_delete_conv())
+
+    async def _do_delete_conv(self) -> None:
+        conv_id = self._current_conv_id
+        if not conv_id:
+            return
+        try:
+            await self._api.delete_conversation(conv_id)
+            self._current_conv_id = None
+            self._current_conv = None
+            self.query_one("#chat-header", Static).update("Kein Chat geöffnet")
+            self.query_one("#message-log", RichLog).clear()
+            await self._load_conversations()
+            self.notify("Chat gelöscht.")
+        except Exception as exc:
+            self.notify(f"Löschen fehlgeschlagen: {exc}", severity="error")
+
     def action_telegram_qr(self) -> None:
         asyncio.create_task(self._generate_telegram_qr())
 
@@ -301,3 +331,22 @@ class MainScreen(Screen):
 
     def action_quit_app(self) -> None:
         self.app.exit()
+
+
+class _ConfirmScreen(ModalScreen[bool]):
+    """Einfacher Ja/Nein-Dialog."""
+
+    def __init__(self, message: str) -> None:
+        super().__init__()
+        self._message = message
+
+    def compose(self) -> ComposeResult:
+        from textual.widgets import Label
+        with Vertical(id="compose-dialog"):
+            yield Label(self._message, id="confirm-msg")
+            with Horizontal(id="compose-buttons"):
+                yield Button("Abbrechen", variant="default", id="btn-no")
+                yield Button("Löschen", variant="error", id="btn-yes")
+
+    def on_button_pressed(self, event: Button.Pressed) -> None:
+        self.dismiss(event.button.id == "btn-yes")