feat(standin-sprites): ✨ Add proof sprite capture script and update sprite UID consistency

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/scenes/tests/standin_sprite_proof.gd.uid

@@ -0,0 +1 @@
+uid://cr36lq2cvnrd3

tools/standin-sprites/capture_proof.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# Render the stand-in sprite proof scene under a headless weston (llvmpipe)
+# virtual display so the in-engine screenshot capture works. Mirrors the
+# RENDER_MODE=weston path in scripts/autoplay/run_ap3.sh.
+#
+# Output: copies user://screenshots/standin_sprite_proof.png to
+#   tools/standin-sprites/standin_sprite_proof.png (and stdout path).
+set -uo pipefail
+
+REPO="$HOME/Code/@projects/@magic-civilization"
+# Args: [scene_basename] [png_basename] [width] [height]
+SCENE_NAME="${1:-standin_sprite_proof}"
+PNG_NAME="${2:-$SCENE_NAME}"
+W="${3:-1280}"
+H="${4:-820}"
+SCENE="res://engine/scenes/tests/${SCENE_NAME}.tscn"
+SOCKET="standin-proof-$$"
+LOGDIR="$(mktemp -d)"
+
+weston --backend=headless --socket="$SOCKET" --width="$W" --height="$H" \
+  >"$LOGDIR/weston.log" 2>&1 &
+WESTON_PID=$!
+trap 'kill "$WESTON_PID" 2>/dev/null || true' EXIT
+sleep 1
+
+cd "$REPO/src/game"
+timeout 90 flatpak run --user \
+  --filesystem=home \
+  --socket=wayland \
+  --env=WAYLAND_DISPLAY="$SOCKET" \
+  --filesystem=xdg-run/"$SOCKET" \
+  org.godotengine.Godot --path . --rendering-method gl_compatibility \
+  "$SCENE" 2>&1 | grep -iE "standin_sprite_proof|MISSING" | head
+
+UD="$HOME/.var/app/org.godotengine.Godot/data/godot/app_userdata/Magic Civilization/screenshots/${PNG_NAME}.png"
+DEST="$REPO/tools/standin-sprites/${PNG_NAME}.png"
+if [ -f "$UD" ]; then
+  cp "$UD" "$DEST"
+  echo "PROOF_OK: $DEST"
+else
+  echo "PROOF_MISSING: screenshot not produced (see $LOGDIR/weston.log)"
+  exit 1
+fi