Implement balance monitoring and notification for Selectel API integration

- Added support for balance tracking using `SELECTEL_API_TOKEN` in the configuration.
- Introduced new balance notification logic in the local watchdog, alerting users on balance changes based on defined thresholds.
- Updated documentation to include instructions for setting up balance notifications and the required environment variables.
- Enhanced the `ready` and `session` modules to initialize balance state and handle notifications during GPU operations.
- Refactored the CLI and related components to support the new balance monitoring features, ensuring a seamless user experience.

tests/test_verify_stack.py

@@ -0,0 +1,55 @@
+from gpu_rent.ready import ServiceCheck, _expected_services, verify_stack_local
+
+
+class _Cfg:
+    enable_swarmui = True
+    llm_runtime = "none"
+    swarmui_local_port = 17801
+    ollama_local_port = 17811
+    llamacpp_local_port = 17812
+
+
+def test_expected_services_swarm_only():
+    assert _expected_services(_Cfg()) == (True, False, False)
+
+
+def test_expected_services_llm_only():
+    class C:
+        enable_swarmui = False
+        llm_runtime = "llamacpp"
+
+    assert _expected_services(C()) == (False, False, True)
+
+
+def test_verify_stack_local_empty_when_nothing():
+    class C:
+        enable_swarmui = False
+        llm_runtime = "none"
+        swarmui_local_port = 17801
+        ollama_local_port = 17811
+        llamacpp_local_port = 17812
+
+    logs: list[str] = []
+    assert verify_stack_local(C(), logs.append, timeout=0.1) == []
+
+
+def test_verify_stack_local_fails_closed_port(monkeypatch):
+    class C:
+        enable_swarmui = False
+        llm_runtime = "ollama"
+        swarmui_local_port = 17801
+        ollama_local_port = 17999
+        llamacpp_local_port = 17812
+
+    monkeypatch.setattr("gpu_rent.ready._tcp_ok", lambda port, host="127.0.0.1", timeout=0.8: False)
+    logs: list[str] = []
+    try:
+        verify_stack_local(C(), logs.append, timeout=0.3, poll_every=0.1)
+        assert False, "expected CloudError"
+    except Exception as exc:
+        assert "ollama" in str(exc).lower() or "не отвечает" in str(exc)
+
+
+def test_service_check_dataclass():
+    c = ServiceCheck("x", True, "ok", "vm")
+    assert c.ok and c.where == "vm"