fix: handle silently ignored errors in migration helper and pipeline cancel

[warren830]

Summary

• In AutoMigrateTables, properly handle db.First errors instead of silently discarding them — NotFound is expected for empty tables but other errors (e.g. connection issues) should be surfaced
• In CancelPipeline, log task cancellation failures instead of silently ignoring them with _ = CancelTask()

Test plan

• Verify AutoMigrateTables works correctly for both empty and populated tables
• Verify pipeline cancellation logs errors for individual task cancel failures
• Verify existing migration scripts still pass