fix(config,simulate): reject output-key collisions and gate simulated rollback on deploy results

[joshua-temple]

Two correctness fixes.

• config: OutputKey() collapses '-' to '' but validation enforced uniqueness on the raw name, so two names differing only by '-' vs '' collapsed to the same emitted GHA output key while passing validation (one silently shadowed the other). validateOutputKeyCollisions now rejects such collisions (builds/deploys/environments), naming both entries and the shared key.
• simulate: the simulate rollback Apply path skipped the deploy-result gate the real rollback finalize enforces, so it modeled a clean revert where the real system would refuse. Simulate now applies the same gateOnDeployResults (with --deployable scoping); a blocked rollback models a gated no-write, not a revert.

Verification: build/-race/lint green, full suite; red-then-green tests for the three collision cases and the gate block/proceed cases. No generated output changed (no shipped manifest collides).