refactor: 统一 DB/Redis 配置为 DSN 模式 + 移除 Helm/K8s 部署

- DatabaseConfig: Host/Port/User/Password/Name/DBName/SSLMode → 单个 DSN 字段
- RedisConfig: Host/Port/Password/DB/URL → 单个 DSN 字段
- 环境变量: GOCHAT_DATABASE_* (7个) → GOCHAT_DATABASE_DSN, GOCHAT_REDIS_* (5个) → GOCHAT_REDIS_DSN
- validator.go: DSN URL 解析校验 (scheme + host)
- redis.go: redis.ParseURL(cfg.DSN) 直连
- 所有 docker-compose / CI / shell 脚本 / .env 同步更新
- 删除 deploy/helm/ 整个目录 (20个文件)
- CI 删除 helm-validate / deploy-staging / deploy-production 三个 job
- 文档同步更新 (README, 架构设计, PRD, 滚动升级)

deploy/docker/docker-compose.prod.yml

@@ -60,10 +60,8 @@ services:
     env_file: ../../.env
     environment:
       - GOCHAT_ENV=production
-      - POSTGRES_HOST=postgres
-      - POSTGRES_PORT=5432
-      - REDIS_HOST=redis
-      - REDIS_PORT=6379
+      - GOCHAT_DATABASE_DSN=postgres://${POSTGRES_USER:-gochat}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB:-gochat_production}?sslmode=disable
+      - GOCHAT_REDIS_DSN=redis://:${REDIS_PASSWORD}@redis:6379
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:3000/health"]
       interval: 30s
@@ -92,10 +90,8 @@ services:
     env_file: ../../.env
     environment:
       - GOCHAT_ENV=production
-      - POSTGRES_HOST=postgres
-      - POSTGRES_PORT=5432
-      - REDIS_HOST=redis
-      - REDIS_PORT=6379
+      - GOCHAT_DATABASE_DSN=postgres://${POSTGRES_USER:-gochat}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB:-gochat_production}?sslmode=disable
+      - GOCHAT_REDIS_DSN=redis://:${REDIS_PASSWORD}@redis:6379
     deploy:
       resources:
         limits: