feat: Implement Phase 2 alerting system with anomaly detection

Proactive monitoring infrastructure for server health:

**Alert Service:**
- Population drop detection (configurable % threshold)
- FPS degradation monitoring (configurable FPS threshold)
- Multi-channel notifications (Discord, Pushbullet, Email)
- Spam prevention (30-min duplicate suppression)
- Severity levels (Info, Warning, Critical)

**Database:**
- alert_config table (thresholds per license)
- alert_history table (event log with metadata)
- 90-day retention with cleanup job

**Integration:**
- Discord/Pushbullet service integration
- Notification config retrieval from public_site_config
- Ready for stats pipeline integration

Purpose: Server admins get alerted when anomalies occur
(population crashes, performance degradation). Configurable
thresholds enable proactive server management.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -4,6 +4,34 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Added (Phase 2 — Alerting System)
+
+**Backend:**
+- Migration 008: Alert configuration and history tables
+  - `alert_config` table with threshold settings per license (population drop %, FPS threshold)
+  - `alert_history` table logging all triggered alerts with metadata
+  - Default alert config created for all existing licenses
+- Alert service (`services/alerting.rs`):
+  - `check_population_anomaly()` — Detects player count drops exceeding threshold
+  - `check_fps_degradation()` — Monitors server performance degradation
+  - Spam prevention (30-minute duplicate suppression)
+  - Multi-channel notifications (Discord + Pushbullet + Email)
+  - Severity levels: Info, Warning, Critical
+- Alert database layer (`db/alerts.rs`):
+  - `get_alert_config()` / `update_alert_config()` — Threshold configuration
+  - `insert_alert()` / `mark_alert_notified()` — Alert history tracking
+  - `check_recent_alert()` — Duplicate detection
+  - `cleanup_old_alerts()` — 90-day retention cleanup
+- Updated `db/notifications.rs` — Notification config retrieval with webhook/API key support
+
+**Alert Types:**
+- Population Drop — Triggers when player count drops >X% in 1 hour
+- FPS Degradation — Triggers when FPS falls below configurable threshold
+- Server Crash — Critical alert for auto-recovery failures
+- Wipe Failed — Alert when wipe execution fails
+
+**Purpose:** Proactive monitoring for server health issues. Alerts server admins via Discord/Pushbullet when anomalies detected (population crashes, performance degradation). Configurable thresholds per license.
+
 ### Added (Phase 2 — Wipe Performance Analytics)
 
 **Backend:**