feat(docker): remove bundled MySQL from production Compose stack

Production installs now run only the Nexus container; MySQL and Redis are self-hosted on the machine or 1Panel, with install wizard defaults pointing at host.docker.internal.

Co-authored-by: Cursor <cursoragent@cursor.com>

docker/.env.prod.example

@@ -1,9 +1,6 @@
 # Production Compose env — copy to docker/.env.prod (never commit)
-# Fresh install: bash deploy/install-nexus-fresh.sh (auto-generates unique secrets per host)
-# Migration: bash deploy/nexus-1panel.sh install --from-env /path/to/old/.env
-
-MYSQL_ROOT_PASSWORD=change_me_root_strong
-MYSQL_PASSWORD=change_me_nexus_strong
+# Fresh install: bash deploy/install-nexus-fresh.sh (auto-generates NEXUS keys per host)
+# MySQL / Redis 不在 Docker 栈 — 请在宿主机或 1Panel 自建，安装向导步骤 3 填写
 
 # Auto-generated on fresh install (unique per server). Do NOT copy between hosts.
 NEXUS_SECRET_KEY=
@@ -17,12 +14,11 @@ NEXUS_INSTALL_WIZARD_PENDING=0
 NEXUS_CORS_ORIGINS=https://api.synaglobal.vip
 NEXUS_API_BASE_URL=https://api.synaglobal.vip
 
-# 2 vCPU / 8 GiB host (matches docker/mysql-prod-2c8g.cnf + compose limits)
+# Nexus container resource profile (docker/profiles/*.env)
 NEXUS_DB_POOL_SIZE=30
 NEXUS_DB_MAX_OVERFLOW=20
 
-# Redis 不在 Docker 栈内 — 请在宿主机或 1Panel 应用商店自行安装
-# Nexus 容器通过 host.docker.internal 访问宿主机 Redis（见 docker-compose.prod.yml）
+# 外置 Redis（宿主机/1Panel），Nexus 容器经 host.docker.internal 访问
 NEXUS_REDIS_URL=redis://host.docker.internal:6379/0
 
 # Optional