feat: initial VPS monitoring platform

- FastAPI backend with auth, server CRUD, metrics collection
- Web dashboard with dark theme, server cards, SSH terminal (xterm.js)
- Telegram bot with inline keyboards, server management, reboot
- Telegram Mini App for mobile monitoring
- Background monitoring via asyncssh (CPU, RAM, Disk, Network, Uptime)
- Alert system with configurable thresholds
- WebSocket SSH terminal in browser
- One-command install script
- Systemd service configuration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/services/alerter.py

@@ -0,0 +1,56 @@
+import logging
+from datetime import datetime
+from typing import Dict
+
+from server.config import load_settings, load_servers
+from server.services.monitor import get_all_metrics
+
+logger = logging.getLogger(__name__)
+
+previous_states: Dict[str, bool] = {}
+
+
+async def check_alerts():
+    """Check metrics against thresholds and send alerts."""
+    from server.services.telegram_bot import send_alert
+
+    settings = load_settings()
+    servers = load_servers()
+    metrics = get_all_metrics()
+
+    cpu_threshold = settings.get("alert_cpu_threshold", 90)
+    ram_threshold = settings.get("alert_ram_threshold", 90)
+    disk_threshold = settings.get("alert_disk_threshold", 90)
+
+    for srv in servers:
+        host = srv["host"]
+        m = metrics.get(host, {})
+        name = srv.get("name", host)
+
+        current_online = m.get("online", False)
+        prev_online = previous_states.get(host)
+
+        # Online/Offline state change
+        if prev_online is not None and prev_online != current_online:
+            if current_online:
+                await send_alert(f"🟢 **{name}** ({host}) — снова онлайн")
+            else:
+                await send_alert(f"🔴 **{name}** ({host}) — OFFLINE!")
+
+        previous_states[host] = current_online
+
+        if not current_online:
+            continue
+
+        # Threshold alerts
+        cpu = m.get("cpu_percent", 0)
+        if cpu >= cpu_threshold:
+            await send_alert(f"⚠️ **{name}** — CPU: {cpu}% (порог: {cpu_threshold}%)")
+
+        ram = m.get("ram_percent", 0)
+        if ram >= ram_threshold:
+            await send_alert(f"⚠️ **{name}** — RAM: {ram}% (порог: {ram_threshold}%)")
+
+        disk = m.get("disk_percent", 0)
+        if disk >= disk_threshold:
+            await send_alert(f"⚠️ **{name}** — Disk: {disk}% (порог: {disk_threshold}%)")