Enhancement: Add system event logging and viewer with M3U/EPG endpoint caching

System Event Logging:
- Add SystemEvent model with 15 event types tracking channel operations, client connections, M3U/EPG activities, and buffering events
- Log detailed metrics for M3U/EPG refresh operations (streams/programs created/updated/deleted)
- Track M3U/EPG downloads with client information (IP address, user agent, profile, channel count)
- Record channel lifecycle events (start, stop, reconnect) with stream and client details
- Monitor client connections/disconnections and buffering events with stream metadata

Event Viewer UI:
- Add SystemEvents component with real-time updates via WebSocket
- Implement pagination, filtering by event type, and configurable auto-refresh
- Display events with color-coded badges and type-specific icons
- Integrate event viewer into Stats page with modal display
- Add event management settings (retention period, refresh rate)

M3U/EPG Endpoint Optimizations:
- Implement content caching with 5-minute TTL to reduce duplicate processing
- Add client-based event deduplication (2-second window) using IP and user agent hashing
- Support HEAD requests for efficient preflight checks
- Cache streamed EPG responses while maintaining streaming behavior for first request

core/models.py

@@ -375,3 +375,43 @@ class CoreSettings(models.Model):
             return rules
         except Exception:
             return rules
+
+
+class SystemEvent(models.Model):
+    """
+    Tracks system events like channel start/stop, buffering, failover, client connections.
+    Maintains a rolling history based on max_system_events setting.
+    """
+    EVENT_TYPES = [
+        ('channel_start', 'Channel Started'),
+        ('channel_stop', 'Channel Stopped'),
+        ('channel_buffering', 'Channel Buffering'),
+        ('channel_failover', 'Channel Failover'),
+        ('channel_reconnect', 'Channel Reconnected'),
+        ('channel_error', 'Channel Error'),
+        ('client_connect', 'Client Connected'),
+        ('client_disconnect', 'Client Disconnected'),
+        ('recording_start', 'Recording Started'),
+        ('recording_end', 'Recording Ended'),
+        ('stream_switch', 'Stream Switched'),
+        ('m3u_refresh', 'M3U Refreshed'),
+        ('m3u_download', 'M3U Downloaded'),
+        ('epg_refresh', 'EPG Refreshed'),
+        ('epg_download', 'EPG Downloaded'),
+    ]
+
+    event_type = models.CharField(max_length=50, choices=EVENT_TYPES, db_index=True)
+    timestamp = models.DateTimeField(auto_now_add=True, db_index=True)
+    channel_id = models.UUIDField(null=True, blank=True, db_index=True)
+    channel_name = models.CharField(max_length=255, null=True, blank=True)
+    details = models.JSONField(default=dict, blank=True)
+
+    class Meta:
+        ordering = ['-timestamp']
+        indexes = [
+            models.Index(fields=['-timestamp']),
+            models.Index(fields=['event_type', '-timestamp']),
+        ]
+
+    def __str__(self):
+        return f"{self.event_type} - {self.channel_name or 'N/A'} @ {self.timestamp}"