e2e: builder-identity gate soft-exits 0 without a session, structurally failing 4 cells on every branch

Since the builder-identity gate landed (b6d21f5, June 17), every CI e2e invocation of deploy/mod hits checkIdentityGate -> not-logged-in -> soft exit 0 with the 'Join the competition first' notice, before env validation, availability, or publish paths run. Result: pr-preflight (banner), pr-login-session, and pr-deploy-frontend fail structurally on every branch - main included: 60/60 main runs red since the gate landed, most recently run 32001119588 (same four cells).

Two remedy options:

1. Seed a test session + on-chain getRootAccount binding for the e2e signer in CI (globalSetup), so the gate passes legitimately.
2. Add a sanctioned gate escape for explicit --suri dev signing (env-gated to CI/test).

Note: one sub-case is already fixed in #498 (52816f9): --env validation now runs before the gate, so an unwired env exits non-zero again. The gate decision itself is a design call - needs an owner.

Start at the deploy/mod e2e entry point and trace checkIdentityGate through the CI setup, including the proposed globalSetup session binding and the --suri dev-signing path. The owner must choose and validate a sanctioned gate behavior so pr-preflight, pr-login-session, and pr-deploy-frontend no longer fail structurally while --env validation still runs.