feat(ui): replace gameplay icons with local SVGs

docs/PLAYER_UI.md

@@ -12,6 +12,20 @@ locally authored `icons.svg` sprite. The deterministic asset build compresses
 each file with gzip for LittleFS. There are no remote fonts, frameworks,
 analytics, icon services, or runtime network dependencies beyond the local ESP.
 
+## Gameplay icon mapping
+
+`icons.svg` contains editable, local SVG symbols with a shared `64 x 64` view
+box for the reference-derived gameplay set: `player`, `key`, `exit-closed`,
+`crystal`, `exit-open`, and `spikes`. Player 1 is yellow and Player 2 is blue;
+their matching keys and exits use the same owner color. The player, key, and
+exit silhouettes remain distinct, and Player 2 uses a dashed secondary
+treatment so ownership does not depend on color alone.
+
+The closed and opened arched exits show the existing locked and opened exit
+states. The crystal represents the existing vision artifact. Spikes appear only
+with local blocked-movement feedback and do not add a trap, damage, protocol,
+or server-state feature.
+
 ## Input contract
 
 Arrow keys and WASD map to `north`, `east`, `south`, and `west` move intentions.