feat: swap the splash banner to an SVG

The PNG banner is replaced by an SVG so the splash artwork scales; the
old aare_banner.png is removed and gui.py loads the .svg path (the
stale path yielded a null splash pixmap).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/aare/gui/gui.py

@@ -21,7 +21,9 @@ def main():
     try:
         basedir = os.path.dirname(__file__)
         icon_path = os.path.join(basedir, "graphics/aaregui_logo.svg")
-        banner_path = os.path.join(basedir, "graphics/aare_banner.png")
+        # The banner is an SVG now; the old aare_banner.png no longer exists
+        # and yielded a null splash pixmap.
+        banner_path = os.path.join(basedir, "graphics/aare_banner.svg")
     except Exception:
         logger.exception("Failed to load resources for splash screen")
         sys.exit(1)