wireReferences() (new, extracted from boot.js's queueInputs) now reports an
unwired count instead of silently losing a reference when: the pipeline has
fewer reference slots than the scene has references, two references' roles
resolve to the same slot or downstream destination, or a reference's slot
was already claimed by the scene's source-image assignment. boot.js toasts
whenever unwired > 0, worded to cover both the capacity and collision cases.
None of these are reachable through the one shipped preset (H3's R2V, one
role per slot) -- all are latent contract violations a hand-edited or future
preset could trigger. 10 new tests in reference_wiring.test.js.
