fix: persist adopted Volcengine ENI IDs

[CMGS]

Summary

• persist the IDs of Volcengine ENIs that contribute addresses to an adopted pool
• let teardown retry detached ENIs by exact ID while leaving unrelated secondary ENIs untouched
• align the pool-state and Volcengine documentation with the new ownership boundary

Why

Without persisted IDs, teardown falls back to listing only ENIs currently attached to the instance. If detach succeeds and delete then fails, the next teardown cannot rediscover that detached ENI and can remove local state while the cloud resource remains.

Verification

• gofmt -d cmd/adopt.go
• git diff --check
• lint, unit tests, and compilation were not run per the static-only review scope