Rename Step Line to Gig Line

Update the game name in project.godot, export presets, UI/marquee/title strings, packaging (AppImage/NSIS/desktop/appdata), tools, docs, and the generated prop GLBs. Packaging assets and README screenshots are regenerated. Headless suite 209/209 and Python tooling tests pass.

tools/publish_release.sh

@@ -59,14 +59,14 @@ fi
 
 # Artifacts that must exist (run tools/build_releases.sh first).
 portables=(
-  "build/step-line-linux-$VERSION.x86_64"
-  "build/step-line-windows-$VERSION.exe"
-  "build/step-line-macos-$VERSION.zip"
+  "build/gig-line-linux-$VERSION.x86_64"
+  "build/gig-line-windows-$VERSION.exe"
+  "build/gig-line-macos-$VERSION.zip"
 )
 extras=(
-  "build/step-line-setup-$VERSION.exe"
-  "build/step-line-$VERSION-x86_64.AppImage"
-  "build/step-line-web-$VERSION.zip"
+  "build/gig-line-setup-$VERSION.exe"
+  "build/gig-line-$VERSION-x86_64.AppImage"
+  "build/gig-line-web-$VERSION.zip"
 )
 all_artifacts=("${portables[@]}")
 for f in "${extras[@]}"; do
@@ -81,7 +81,7 @@ API="$HOST/api/v1/repos/$REPO/releases"
 echo "==> Creating release $TAG on $HOST/$REPO"
 RELEASE_ID="$(curl -s -X POST "$API" "${AUTH[@]}" \
   -H "Content-Type: application/json" \
-  -d "{\"tag_name\":\"$TAG\",\"name\":\"$TAG\",\"body\":\"Step Line $VERSION — playable prototype. See README for controls.\",\"draft\":false,\"prerelease\":false}" \
+  -d "{\"tag_name\":\"$TAG\",\"name\":\"$TAG\",\"body\":\"Gig Line $VERSION — playable prototype. See README for controls.\",\"draft\":false,\"prerelease\":false}" \
   | python3 -c "import sys,json;print(json.load(sys.stdin).get('id',''))" 2>/dev/null || true)"
 
 # If the release already exists (tag already pushed), reuse it.