feat: Telegram QR-Code Invite-Link + WhatsApp Empfang-Fix

Telegram:
- /start <contact_id> Deep-Link Handler: verknüpft Kontakt automatisch mit chat_id
- QR-Code Endpunkt GET /api/v1/contacts/{id}/telegram-qr (PNG)
- TUI: Taste T öffnet QR-Code im Browser (HTML mit eingebettetem PNG)
- config.py + .env.example: TELEGRAM_BOT_USERNAME=mcm_bot
- qrcode[pil] zu requirements.txt hinzugefügt

WhatsApp:
- receiveTimeout 5→3s, HTTP-Timeout 8s → verhindert Polling-Overlap

channels/telegram_channel.py

@@ -5,7 +5,7 @@ import logging
 from typing import TYPE_CHECKING, Any, Callable, Awaitable
 
 from telegram import Update
-from telegram.ext import Application, ApplicationBuilder, MessageHandler, filters
+from telegram.ext import Application, ApplicationBuilder, CommandHandler, MessageHandler, filters
 
 from channels.base import BaseChannel
 from config import settings
@@ -62,6 +62,7 @@ class TelegramChannel(BaseChannel):
             return
 
         self._app = ApplicationBuilder().token(settings.telegram_token).build()
+        self._app.add_handler(CommandHandler("start", self._handle_start))
         self._app.add_handler(MessageHandler(~filters.COMMAND, self._handle_message))
 
         await self._app.initialize()
@@ -97,6 +98,31 @@ class TelegramChannel(BaseChannel):
         except Exception as exc:
             logger.error("Telegram polling error: %s", exc)
 
+    async def _handle_start(self, update: Update, context: Any) -> None:
+        """Verarbeitet /start [contact_id] — verknüpft Kontakt mit chat_id."""
+        if not update.message or not self._inbound_callback:
+            return
+        msg = update.message
+        args = context.args  # Liste der Parameter nach /start
+        contact_id = args[0] if args else None
+
+        payload: dict[str, Any] = {
+            "channel": "telegram",
+            "channel_message_id": str(msg.message_id),
+            "sender_telegram_id": str(msg.from_user.id) if msg.from_user else None,
+            "sender_name": (
+                (msg.from_user.full_name or msg.from_user.username)
+                if msg.from_user
+                else "Unknown"
+            ),
+            "chat_id": str(msg.chat.id),
+            "text": "/start",
+            "reply_to_id": None,
+            "link_contact_id": contact_id,  # Kontakt aus QR-Code verknüpfen
+        }
+        await self._inbound_callback(payload)
+        await msg.reply_text("Willkommen! Sie sind jetzt mit MCM verbunden.")
+
     async def _handle_message(self, update: Update, context: Any) -> None:
         if not update.message or not self._inbound_callback:
             return

channels/whatsapp_channel.py

@@ -85,7 +85,8 @@ class WhatsAppChannel(BaseChannel):
             return
         url = f"{self._base_url}/receiveNotification/{self._token}"
         try:
-            async with self._get_session().get(url, params={"receiveTimeout": 5}) as resp:
+            timeout = aiohttp.ClientTimeout(total=8)
+            async with self._get_session().get(url, params={"receiveTimeout": 3}, timeout=timeout) as resp:
                 if resp.status != 200:
                     return
                 data = await resp.json()