test(environment): 1058 migration three-state verification on real postgres

- fresh database, legacy upgrade (rows get one-shot access key, online=false),
  repeat startup idempotence
- 1058 revised before any database applied it: drop dead token column,
  provision access_key via temporary default so non-empty legacy tables upgrade
- immutable-migration rule skips PR-local migrations until merged; after merge
  the lock applies again

internal/environment/migrations/1058_gateway_outbound_channel.sql

@@ -6,7 +6,8 @@ ALTER TABLE gateway
     DROP COLUMN health_status,
     DROP COLUMN last_check_reason,
     DROP COLUMN last_checked_at,
-    ADD COLUMN access_key text NOT NULL,
+    DROP COLUMN token,
+    ADD COLUMN access_key text NOT NULL DEFAULT '',
     ADD COLUMN online boolean NOT NULL DEFAULT false,
     ADD COLUMN last_seen_at timestamptz,
     ADD COLUMN version text NOT NULL DEFAULT '';
@@ -14,6 +15,7 @@ ALTER TABLE gateway
 -- 既有网关记录补一个一次性访问密钥（随机 48 位十六进制），新网关由平台生成。
 UPDATE gateway SET access_key = encode(sha256(('creator-hub-gateway-' || id::text || random()::text)::bytea), 'hex')
 WHERE access_key = '';
+ALTER TABLE gateway ALTER COLUMN access_key DROP DEFAULT;
 
 -- 统一任务模型：所有平台→网关通信都是持久化任务；全量任务即执行记录。
 CREATE TABLE gateway_task (