feat(api): 接入微信登录并原生实现咨询域（ECR-049/050）

小程序可在 Go 上完成微信手机号登录、测评、预约和下单，不再反代 Java。

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

apps/api/migrations/000058_wechat_auth_gateway.up.sql

@@ -0,0 +1,10 @@
+-- ECR-049: WeChat identity + Java consult token on session
+
+ALTER TABLE users ADD COLUMN IF NOT EXISTS wx_openid varchar(64) NULL;
+ALTER TABLE users ADD COLUMN IF NOT EXISTS wx_unionid varchar(64) NULL;
+ALTER TABLE users ADD COLUMN IF NOT EXISTS java_platform_user_id bigint NULL;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_users_wx_openid_unique
+  ON users(wx_openid) WHERE wx_openid IS NOT NULL AND deleted_at IS NULL;
+
+ALTER TABLE user_sessions ADD COLUMN IF NOT EXISTS java_access_token text NULL;