Tune the startup page (index.html): Load-Screen.png height,
Play As Guest / Login hit areas (% of the art frame),
and carousel ← / → + play buttons (% of the carousel area below the art).
Background matches production via main_screen_v2_layout.json.
Saves to data/load_screen_layout.json — click Save now then hard-refresh
index.html (Ctrl+Shift+R) so live matches the tuner.
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