Add real-time log monitoring and system stats dashboard

Implements a comprehensive monitoring system for the admin interface:

Backend:
- New monitoring package with Redis ring buffer for log storage
- Zerolog MultiWriter to capture logs to Redis
- System stats collection (CPU, memory, disk, goroutines, GC)
- HTTP metrics middleware (request counts, latency, error rates)
- Asynq queue stats for worker process
- WebSocket endpoint for real-time log streaming
- Admin auth middleware now accepts token in query params (for WebSocket)

Frontend:
- New monitoring page with tabs (Overview, Logs, API Stats, Worker Stats)
- Real-time log viewer with level filtering and search
- System stats cards showing CPU, memory, goroutines, uptime
- HTTP endpoint statistics table
- Asynq queue depth visualization
- Enable/disable monitoring toggle in settings

Memory safeguards:
- Max 200 unique endpoints tracked
- Hourly stats reset to prevent unbounded growth
- Max 1000 log entries in ring buffer
- Max 1000 latency samples for P95 calculation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

cmd/api/main.go

@@ -15,6 +15,7 @@ import (
 	"github.com/treytartt/casera-api/internal/config"
 	"github.com/treytartt/casera-api/internal/database"
 	"github.com/treytartt/casera-api/internal/i18n"
+	"github.com/treytartt/casera-api/internal/monitoring"
 	"github.com/treytartt/casera-api/internal/push"
 	"github.com/treytartt/casera-api/internal/router"
 	"github.com/treytartt/casera-api/internal/services"
@@ -29,7 +30,7 @@ func main() {
 		os.Exit(1)
 	}
 
-	// Initialize logger
+	// Initialize basic logger first (will be enhanced after Redis connects)
 	utils.InitLogger(cfg.Server.Debug)
 
 	// Initialize i18n
@@ -80,6 +81,27 @@ func main() {
 		defer cache.Close()
 	}
 
+	// Initialize monitoring service (if Redis is available)
+	var monitoringService *monitoring.Service
+	if cache != nil {
+		monitoringService = monitoring.NewService(monitoring.Config{
+			Process:     "api",
+			RedisClient: cache.Client(),
+			DB:          db, // Pass database for enable_monitoring setting sync
+		})
+
+		// Reinitialize logger with monitoring writer
+		utils.InitLoggerWithWriter(cfg.Server.Debug, monitoringService.LogWriter())
+
+		// Start stats collection
+		monitoringService.Start()
+		defer monitoringService.Stop()
+
+		log.Info().
+			Bool("log_capture_enabled", monitoringService.IsEnabled()).
+			Msg("Monitoring service initialized")
+	}
+
 	// Initialize email service
 	var emailService *services.EmailService
 	log.Info().
@@ -133,13 +155,14 @@ func main() {
 
 	// Setup router with dependencies (includes admin panel at /admin)
 	deps := &router.Dependencies{
-		DB:             db,
-		Cache:          cache,
-		Config:         cfg,
-		EmailService:   emailService,
-		PDFService:     pdfService,
-		PushClient:     pushClient,
-		StorageService: storageService,
+		DB:                db,
+		Cache:             cache,
+		Config:            cfg,
+		EmailService:      emailService,
+		PDFService:        pdfService,
+		PushClient:        pushClient,
+		StorageService:    storageService,
+		MonitoringService: monitoringService,
 	}
 	r := router.SetupRouter(deps)