test(visual): a shadow-gap measurement, and the spawn height cleared

Tools/shadow_gap.py measures the vertical pixel gap between an object's lowest pixels and the
top of its shadow, as a fraction of the object's height, and calls it contact or floating. It
classifies a shadow by per-channel scaling - a shadow darkens every channel by the same
proportion, an object does not - which separates the two where an absolute delta cannot. Four
unit tests cover contact, floating, an empty box and the border median.

On the real spawn view it returns 'unknown': the crop contains two surfaces (pale wall behind,
dark road below) and one global background cannot classify both. Recorded as the next step, not
presented as working.

The spawn height is measured and cleared: tracing down from 30 m, the topmost surface under the
player is Z 366 and the capsule's feet are at 369 - 3 cm, the capsule skin. If the character
still reads as floating, the gap is between the rendered pavement and its collision surface, not
the spawn Z, and that is what to measure next.

Tools/README.md

@@ -99,6 +99,7 @@ Geographic tools live in [`Geo/tools/`](../Geo/README.md) and the Blender-side b
 | `vehicle_from_template.py` | Converts the owner's `hot hatch.blend` into UE-ready assets: normalises the scale to a documented 4.05 m, splits systems (body/trim/glass/lights/wheels), adds a `UCX_` hull, decimates two LODs, exports FBX per system and writes a report. | `--out`, `--report` | `blender -b "Art/blender/vehicle/hot hatch.blend" --python Tools/vehicle_from_template.py -- --out /tmp/gigline/hatch` |
 | `blender_screenshots.py` | Renders review screenshots out of a .blend: one per mesh object (`--mode objects`) and four turntable angles (`--mode scene`), framed from the scene's own bounds, into `Screenshots/blender/`. | `--label`, `--mode`, `--out`, `--report` | `blender -b "Art/blender/vehicle/hot hatch.blend" --python Tools/blender_screenshots.py -- --label vehicle --mode both` |
 | `build_comparison_md.py` | Regenerates the `Blender vs in-game` section of `Screenshots/README.md` between `<!-- blender-comparison:begin/end -->` markers: in-game captures beside their Blender renders in one table, plus a signoff table with one row per in-game screen. Pairs by name with an alias map for camera-named shots. Run it after every capture or Blender render. | (no arguments) | `python3 Tools/build_comparison_md.py` |
+| `shadow_gap.py` | Measures the vertical pixel gap between an object's lowest pixels and the top of its shadow, as a fraction of the object's height, and calls it `contact` or `floating`. Objective replacement for asking a vision model whether something floats. | `--image`, `--object-box`, `--gap-fraction`, `--out` | `python3 Tools/shadow_gap.py --image Screenshots/demo/review-demo-spawn-view.png --object-box 0.44,0.48,0.60,0.99` |
 
 ## Tests