TarjetaEmisora had the only good fallback for a station with no artwork --
a deterministic pick from 4 bundled illustrations with a gradient/glyph
last resort. FilaEmisoraPlana's flat rows, the Escuchar hero, the "Tus
emisoras" grid cell, the mini player and the full player each had their
own, separate, flat primaryContainer square instead.
Extract the good fallback into PluriStationArtFallback and use it from
every one of those call sites. The selection formula (asset order,
codeUnits-sum modulo) is preserved exactly, since navegacion_auto.dart
mirrors the same formula independently for Android Auto's own drawable
rotation.
The prototype's station thumbnail is a plain 44-48px square, radius
11/12, with no ring or glow (t4 lines 84, 175, 227, 302, 614).
TarjetaEmisora's compact row variant instead painted a 58x58 circle
wrapped in a SweepGradient ring (magenta/cyan/coral) and a 22-blur
glow behind a 50x50 ClipRRect(18).
Replace it with a 48x48 ClipRRect(12) square. Update the loading
shimmer placeholder to match (was also a 58x58 circle block).
S6, Tier 1 visual-fidelity pass (audit id 2521).
FreeTLab