feat(client): add watchdog and disconnect flap handling

Introduce an active watchdog that probes the Telegram client to detect
zombie sessions and restart them in‑process. Add configurable disconnect
flap detection with a sliding window to trigger restarts after repeated
disconnects. New environment variables and config entries are added, and
the Kurigram dependency is now version‑pinned.

tests/mock_config.py

@@ -20,4 +20,11 @@ def get_settings():
         "show_post_flags": True,
         "proxy": None,
         "trusted_proxies": [],
-    }
+        "tg_watchdog_enabled": True,
+        "tg_watchdog_interval": 60,
+        "tg_watchdog_timeout": 10,
+        "tg_watchdog_failures": 3,
+        "tg_watchdog_restart_timeout": 90,
+        "tg_disconnect_flap_limit": 3,
+        "tg_disconnect_flap_window": 120,
+    }