First time the full 3D pipeline (visibility flood-fill -> geometry emit ->
view matrix -> vertex transform -> near-clip -> software span rasterizer)
puts textured tiles on the actual display.

Reached by fixing five stacked blockers in the rasterizer path (see
commit 021bad2): raster_textured_span's char*/signed-index variable
merge, the non-contiguous vertex/rect scalar structs in
render_visible_tile_list, undersized edge records in raster_triangle,
the stubbed float-compare ordinals, and the zeroed viewport clip rect.

Run: UW_ENABLE_3D_GEOMETRY=1 UW_HACK_PITCH=256 with scratchpad/demo_geo.txt

Still off-calibration (needs the pitch hack; real camera-pitch source
unrecovered) -- tracked in memory.md UPDATE 6.