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.

.gitea/workflows/build.yml

@@ -84,19 +84,19 @@ jobs:
           # NOTE: on Linux, makensis uses -D defines (the /D form is Windows-only
           # and is rejected as a script path), and it resolves relative paths
           # against the script directory — pass absolute paths from the workspace.
-          cp assets/textures/icon.ico packaging/windows/step-line.ico
+          cp assets/textures/icon.ico packaging/windows/gig-line.ico
           makensis \
             -DVERSION="$VERSION" \
-            -DARTIFACT="$PWD/build/step-line-windows-$VERSION.exe" \
-            -DICON="$PWD/packaging/windows/step-line.ico" \
-            -DOUT="$PWD/build/step-line-setup-$VERSION.exe" \
-            packaging/windows/step-line.nsi
+            -DARTIFACT="$PWD/build/gig-line-windows-$VERSION.exe" \
+            -DICON="$PWD/packaging/windows/gig-line.ico" \
+            -DOUT="$PWD/build/gig-line-setup-$VERSION.exe" \
+            packaging/windows/gig-line.nsi
 
       - name: Verify Windows installer contents
         run: |
           VERSION="$(sed -n 's/.*config\/version="\([^"]*\)".*/\1/p' project.godot)"
-          ls -la build/step-line-setup-$VERSION.exe
-          7z l build/step-line-setup-$VERSION.exe | grep -E "step-line.exe|uninstall.exe"
+          ls -la build/gig-line-setup-$VERSION.exe
+          7z l build/gig-line-setup-$VERSION.exe | grep -E "gig-line.exe|uninstall.exe"
 
       - name: Package Linux AppImage
         run: |
@@ -106,7 +106,7 @@ jobs:
         if: github.event_name == 'workflow_dispatch'
         uses: actions/upload-artifact@v4
         with:
-          name: step-line-build
+          name: gig-line-build
           path: build/*
           if-no-files-found: error