feat: implement horizontal scaling optimizations for authz service

- Add /health and /ready endpoints for load balancer health checks
- Replace in-memory JWT token cache with Redis for multi-replica support
- Reduce DB connection pool from 100 to 25 connections per replica
- Add distributed rate limiting (100 req/min + 20 burst) using Redis
- Implement circuit breakers for DB and Redis to prevent cascading failures

This enables the service to scale horizontally with multiple replicas
behind a load balancer without exhausting database connections or
maintaining separate token caches per instance.

handlers/health.go

@@ -0,0 +1,84 @@
+package handlers
+
+import (
+	"authorization/db"
+	"authorization/models"
+	"authorization/redisclient"
+	"context"
+	"encoding/json"
+	"net/http"
+	"time"
+)
+
+// HealthHandler provides a basic liveness check
+// @Summary Health check endpoint
+// @Description Returns service health status for load balancer health checks
+// @Tags health
+// @Produce json
+// @Success 200 {object} HealthResponse
+// @Router /health [get]
+func HealthHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	json.NewEncoder(w).Encode(models.HealthResponse{
+		Status: "ok",
+	})
+}
+
+// ReadyHandler checks if the service is ready to handle requests
+// @Summary Readiness check endpoint
+// @Description Returns readiness status including database and Redis connectivity
+// @Tags health
+// @Produce json
+// @Success 200 {object} HealthResponse
+// @Failure 503 {object} HealthResponse
+// @Router /ready [get]
+func ReadyHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+
+	services := make(map[string]string)
+	allHealthy := true
+
+	// Check database
+	if db.DB != nil {
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel()
+		if err := db.DB.PingContext(ctx); err != nil {
+			services["database"] = "unhealthy"
+			allHealthy = false
+		} else {
+			services["database"] = "healthy"
+		}
+	} else {
+		services["database"] = "not_initialized"
+		allHealthy = false
+	}
+
+	// Check Redis
+	if redisclient.RDB != nil {
+		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+		defer cancel()
+		if _, err := redisclient.RDB.Ping(ctx).Result(); err != nil {
+			services["redis"] = "unhealthy"
+			allHealthy = false
+		} else {
+			services["redis"] = "healthy"
+		}
+	} else {
+		services["redis"] = "not_initialized"
+		allHealthy = false
+	}
+
+	status := "ready"
+	statusCode := http.StatusOK
+	if !allHealthy {
+		status = "not_ready"
+		statusCode = http.StatusServiceUnavailable
+	}
+
+	w.WriteHeader(statusCode)
+	json.NewEncoder(w).Encode(models.HealthResponse{
+		Status:   status,
+		Services: services,
+	})
+}