Adds a new diagnostic flag for the indoor-walking walk-miss probe
spike per docs/superpowers/specs/2026-05-21-indoor-walk-miss-probe-design.md.
Env var ACDREAM_PROBE_WALK_MISS=1, runtime-toggleable via property.
No DebugPanel mirror — spike-only. Following commits wire the
[walk-miss] and [floor-polys] emissions to this flag.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
