CoderWorkspacePool: count bound and used members only when their owner matches the pool's owner #465

Problem

The pool counts a bound or used member toward its bound and used counts without checking that the member's spec.ownerID matches the pool's resolved owner. countPoolMembers (internal/controller/coderworkspacepool_controller.go:767-780) increments both counts before it checks any owner ID.

The #153 plan lists this as optional hardening (section 16, item 777(c) of the #357 final assessor items). The #463 round-2 verifier found it unimplemented and untracked.

Impact

Low. Users have read-only RBAC on members (threat T4), so only the operator or a cluster admin can create a member whose owner differs from its pool. Such a member can skew readyReplicas, boundReplicas or usedReplicas and the replacement decisions that use them.

Fix

Count a bound or used member only when its spec.ownerID equals the pool's resolved owner ID. Add an envtest with a foreign-owner bound member.

Refs #153.

Generated with xum • Model: anthropic:claude-opus-5-5 • Thinking: high