feat: initial commit — backend API + student cabinet frontend

- Go backend: auth (JWT), points earn/spend, QR token generation,
  partners, admin grant/stats endpoints with chi router
- Next.js 14 frontend: login, student dashboard, transaction history,
  QR display, partners list
- PostgreSQL migrations (4 tables), Redis cache, Docker Compose
- CORS middleware, role-based route protection, Zustand auth store

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

backend/pkg/cache/redis.go

@@ -0,0 +1,23 @@
+// Package cache provides Redis client initialization.
+package cache
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/redis/go-redis/v9"
+)
+
+// NewClient creates and validates a Redis client using the given REDIS_URL.
+// Returns an error if the URL cannot be parsed or if the initial PING fails.
+func NewClient(ctx context.Context, redisURL string) (*redis.Client, error) {
+	opts, err := redis.ParseURL(redisURL)
+	if err != nil {
+		return nil, fmt.Errorf("cache.NewClient: parse URL: %w", err)
+	}
+	client := redis.NewClient(opts)
+	if err := client.Ping(ctx).Err(); err != nil {
+		return nil, fmt.Errorf("cache.NewClient: ping: %w", err)
+	}
+	return client, nil
+}