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.

src/gpu_rent/local_watchdog.py

@@ -271,7 +271,8 @@ def install_watchdog(
     log(
         f"local-watchdog установлен ({platform}): тик каждые {interval} мин. "
         f"Grace {grace_seconds() // 60} мин после смерти процесса туннеля → stop. "
-        f"Ctrl+C на туннеле GPU не гасит."
+        f"Ctrl+C на туннеле GPU не гасит. "
+        "При SELECTEL_API_TOKEN — toast каждые BALANCE_NOTIFY_STEP_RUB ₽ (дефолт 200)."
     )
     return marker
 
@@ -314,9 +315,64 @@ def watchdog_status_lines() -> list[str]:
             f"pid={lease.pid} alive={alive} hb={lease.heartbeat_at}"
         )
     lines.append(f"grace: {grace_seconds() // 60} мин (LOCAL_WATCHDOG_GRACE_MINUTES)")
+    try:
+        from gpu_rent.balance import load_balance_state
+
+        bal = load_balance_state()
+        if bal:
+            lines.append(
+                f"balance: baseline {bal.baseline_rub:.0f} ₽ "
+                f"last={bal.last_balance_rub} step_notified={bal.last_notified_step}"
+            )
+        else:
+            lines.append("balance: нет baseline (появится на up при SELECTEL_API_TOKEN)")
+    except Exception:
+        pass
     return lines
 
 
+def check_balance_on_tick(cfg: Config, *, log: Log = print) -> list[str]:
+    """Fetch balance; toast on each BALANCE_NOTIFY_STEP_RUB spent since baseline.
+
+    No-op without SELECTEL_API_TOKEN. Arms baseline on first successful fetch
+    if missing but a GPU session may be running.
+    """
+    from gpu_rent.balance import (
+        BalanceWatchState,
+        fetch_balance_rub,
+        load_balance_state,
+        plan_balance_notices,
+        save_balance_state,
+    )
+    from gpu_rent.notify import notify_message
+
+    token = (cfg.selectel_api_token or "").strip()
+    if not token:
+        return []
+    step = float(cfg.balance_notify_step_rub or 200.0)
+    low = float(cfg.balance_notify_low_rub or 0.0)
+    try:
+        current = fetch_balance_rub(token)
+    except Exception as exc:
+        log(f"balance: {exc}")
+        return []
+
+    state = load_balance_state()
+    if state is None:
+        state = BalanceWatchState(baseline_rub=current, last_balance_rub=current)
+        save_balance_state(state)
+        log(f"balance: baseline {current:.0f} ₽ (шаг {step:.0f} ₽)")
+        return []
+
+    state, messages = plan_balance_notices(
+        state, current, step_rub=step, low_rub=low
+    )
+    save_balance_state(state)
+    for msg in messages:
+        notify_message("gpu-rent баланс", msg, log)
+    return messages
+
+
 def run_tick(*, dry_run: bool = False, log: Log = print) -> TickDecision:
     from gpu_rent.session import cmd_stop
     from gpu_rent.state import load_state
@@ -331,6 +387,18 @@ def run_tick(*, dry_run: bool = False, log: Log = print) -> TickDecision:
         process_alive=pid_alive(lease.pid if lease else None),
         grace_sec=grace_seconds(),
     )
+
+    # Balance steps run on every tick while watchdog is installed (same timer).
+    if watchdog_installed() and not dry_run:
+        try:
+            from gpu_rent.config import load_config
+
+            cfg = load_config(require_auth=False)
+            if state.server_id or (lease and lease.armed):
+                check_balance_on_tick(cfg, log=log)
+        except Exception as exc:
+            log(f"balance tick: {exc}")
+
     if decision.kind == "noop":
         log(f"watchdog tick: noop ({decision.detail})")
         return decision