Reopen public signup: the edge gate comes down only when a fresh account is provably bounded #663

Signup is currently refused at the edge (an IngressRoute in gitops) because a fresh account today can cause a run that spends the owner's model credential. This issue is the reopening: delete the edge gate and let the forge's own signup setting govern, once a fresh outsider account provably cannot spend the owner's budget, run code or apps without bounded resources and isolation, read anything private, or steer anyone's crew.

Already true today (verified): a fresh account cannot read any private repository, app, preview, usage, secret or subscription.

Acceptance criteria

• [ ] Every issue this one is blocked by is closed.
• [ ] An "outsider suite" runs in the gate and in the release smoke test: it signs up a fresh account against the running forge and proves each forbidden thing is refused — no spend of the owner's credential, no run or app without a bounded, isolated resource, no read of anything private, no steering of another repository's crew, and the per-account quotas hold.
• [ ] The edge gate is removed: delete signup-gate.yaml from trevato-apps/gitops apps/forge/prod and its kustomization entry, and delete the forge-signup-gate* objects in the namespace. The forge's own signup setting then governs.
• [ ] A person reads the suite's result and flips signup to open.

Since 2026-10-05 a second edge rule pauses paid and code-running actions for new accounts: trevato-apps/gitops apps/forge/prod/outsider-gate.yaml (commit 6f61adb). Reopening removes it together with signup-gate.yaml (delete the forge-outsider-gate* objects too). The one-way-in rule (#668) is now a blocker: the edge sign-in must not create accounts outside the signup rules before the gates come down.