Port CEnvCell::find_visible_child_cell @ 0x0052dc50 (pseudo_c:311397): walk
rootId's StabList + the root itself, return the first EnvCell whose
PointInCell is true for worldPoint. Used to resolve the camera cell in
3rd-person from the physics cell graph rather than a fresh AABB reclassification.
Root is always the player cell (preserves U.4c flap fix). Returns null when
no stab-list cell or root itself contains the query point.
Confirmed (T3.3 Step 1): no production call site uses FindCameraCell for the
camera projection — the only AABB camera resolver is now deleted (T3.1).
FindVisibleChildCell is wired implicitly via Stage 4 (camera-outside-door scenario);
no GameWindow call site needed in Stage 3.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>