qa: make the demo walkable — terrain collision root cause, spawn, scripted QA

The reported fall-through was a misdiagnosis: the player never fell. The
imported Terrain_DEM had only a bounding-box simple collision proxy, so a
downward trace anywhere in the block hit the terrain at Z 819 (the mesh
bbox max) and the street sat under an invisible 8 m lid. Standing on that
box looked plausible, which is why it read as working.

- add UGigLineAssetTools (C++): force CTF_UseComplexAsSimple on a static
  mesh. UE 5.8 dropped bUseComplexAsSimpleCollision and Python cannot set
  the flag; the builder also saves the asset, since the flag lives there
  and a map-only save silently reverts it.
- spawn (-13336, -1150, 600): inside the carved corridor (the cut is a
  10.7 m half-width around the road centreline), lands on the road at 456.
- fix ResetToStart returning to the mid-air PlayerStart captured in
  BeginPlay: StartLocation is now captured on the first grounded frame.
- HighResShot 1280x720 instead of "1280 720", which is a multiplier.
- add -qaselftest: scripted walk/reset/pause on a core ticker plus a
  swept ground transect. Results: walk 746 cm/2 s with Z steady, reset
  0 cm from spawn, pause/unpause 1/0, transect 84 samples 0 holes.
- rebase onto main, keeping the frontage materials and placement fixes.

Tools/README.md

@@ -51,3 +51,10 @@ Geographic tools live in [`Geo/tools/`](../Geo/README.md) and the Blender-side b
 | --- | --- |
 | `render_screenshots.py` / `render_screenshots.sh` | Rebuilds the review map, runs the game, captures the shot list into `Screenshots/` |
 | `judge_screenshot.py` | Vision-model pre-check: judges a screenshot against an expected-scene description (`--image` + `--expect`, or `--shots` for every shot in the README). Reads `OPENROUTER_API_KEY` from `.env` (ignored). Optional helper — a human must still approve. |
+
+## Gameplay QA
+
+| Command | Purpose |
+| --- | --- |
+| `UnrealEditor <uproject> /Game/Hollywood/DemoMap -game -qaselftest` | Headless behaviour check: drives forward input for 2 s, then resets and pauses. Logs `GigLine QA: ... PASS/FAIL` lines and a final `RESULT`. Runs only with `-qaselftest`, so normal play is unaffected. |
+| `GigLine SIM` / `GigLine GROUND` log lines | Emitted every second by `AGigLineCharacter` (TEMP QA): position, fall state, movement mode, and what the ground probe hits underneath. Remove before release. |