Fix cascading deletion gaps for user and team cleanup

- Add ON DELETE CASCADE to users_teams, oauth_providers, admin_permissions
  and ON DELETE SET NULL (with nullable columns) to team_api_keys.created_by,
  hosts.created_by, host_tokens.created_by so HardDeleteExpiredUsers no longer
  fails with FK violations
- User account deletion now cascades to sole-owned teams via DeleteTeamInternal,
  preventing orphaned teams with live sandboxes after account removal
- ListActiveSandboxesByTeam now includes hibernated sandboxes so their disk
  snapshots are cleaned up during team deletion
- Team soft-delete now hard-deletes sandbox metric points, metric snapshots,
  API keys, and channels to prevent data accumulation on deleted teams
- Extract deleteTeamCore() to deduplicate shared logic across DeleteTeam,
  AdminDeleteTeam, and DeleteTeamInternal
- Fix ListAPIKeysByTeamWithCreator to use LEFT JOIN after created_by became
  nullable, and update handler to read pgtype.Text.String for creator_email

pkg/db/sandboxes.sql.go

@@ -190,7 +190,7 @@ func (q *Queries) InsertSandbox(ctx context.Context, arg InsertSandboxParams) (S
 
 const listActiveSandboxesByTeam = `-- name: ListActiveSandboxesByTeam :many
 SELECT id, team_id, host_id, template, status, vcpus, memory_mb, timeout_sec, disk_size_mb, guest_ip, host_ip, created_at, started_at, last_active_at, last_updated, template_id, template_team_id, metadata FROM sandboxes
-WHERE team_id = $1 AND status IN ('running', 'paused', 'starting')
+WHERE team_id = $1 AND status IN ('running', 'paused', 'starting', 'hibernated')
 ORDER BY created_at DESC
 `