feat(backend): bootstrap Go module, config, and data plane

Introduce configuration validation, Postgres migrations, Redis/storage adapters, and the seed sample video.

backend/internal/redisdb/redis.go

@@ -0,0 +1,26 @@
+package redisdb
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/redis/go-redis/v9"
+)
+
+type Client struct {
+	rdb *redis.Client
+}
+
+func Connect(ctx context.Context, url string) (*Client, error) {
+	opts, err := redis.ParseURL(url)
+	if err != nil {
+		return nil, fmt.Errorf("parse redis url: %w", err)
+	}
+	rdb := redis.NewClient(opts)
+	if err := rdb.Ping(ctx).Err(); err != nil {
+		return nil, fmt.Errorf("ping redis: %w", err)
+	}
+	return &Client{rdb: rdb}, nil
+}
+
+func (c *Client) RDB() *redis.Client { return c.rdb }