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/generate_textures.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Generate small authored textures for Step Line (assets/ import convention).
+"""Generate small authored textures for Gig Line (assets/ import convention).
 
 All outputs are deterministic (fixed seeds), <=1024px, power-of-two where
 possible. Run from the repo root:  python3 tools/generate_textures.py
@@ -202,8 +202,8 @@ def awning():
     for x in range(0, w, 32):
         d.arc([x, h - 24, x + 32, h + 40], 0, 180, fill=(80, 20, 24), width=6)
     f = font(96)
-    tw = d.textlength("STEP LINE", font=f)
-    d.text(((w - tw) / 2, 30), "STEP LINE", font=f, fill=(255, 250, 235))
+    tw = d.textlength("GIG LINE", font=f)
+    d.text(((w - tw) / 2, 30), "GIG LINE", font=f, fill=(255, 250, 235))
     # subtle top shading
     shade = Image.new("RGBA", (w, h), (0, 0, 0, 0))
     sd = ImageDraw.Draw(shade)
@@ -409,7 +409,7 @@ def generate_image(prompt: str, model: str, size: int,
             "Authorization": f"Bearer {_api_key()}",
             "Content-Type": "application/json",
             "HTTP-Referer": "https://git.allucanget.biz/zwitschi/security-game",
-            "X-Title": "Step Line",
+            "X-Title": "Gig Line",
         },
         method="POST",
     )
@@ -472,7 +472,7 @@ def _run_ai(args: argparse.Namespace) -> None:
 
 def _build_arg_parser() -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser(
-        description="Generate Step Line textures (authored or via OpenRouter).")
+        description="Generate Gig Line textures (authored or via OpenRouter).")
     parser.add_argument(
         "--ai", action="store_true",
         help="generate textures through the OpenRouter image API "