add tools/build-vanilla-pack.sh to build the runtime resource pack from Mojang's client jar

tools/build-vanilla-pack.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# Builds the runtime resource pack PixelPics renders from (blockstates, models, textures, items,
+# atlases, font) straight from Mojang's CLIENT jar — no launcher install needed. The plugin ships no
+# assets itself; drop the resulting zip into plugins/PixelPics/resourcepack/. Run it once per
+# Minecraft update. No pack.mcmeta needed (the client jar has none; the loader detects the pack by
+# its assets/minecraft/blockstates folder).
+#
+# Needs: curl, jq, unzip, zip.
+#
+# Usage:  tools/build-vanilla-pack.sh 26.3              # -> ./vanilla-26.3.zip
+#         tools/build-vanilla-pack.sh 26.3 <output-dir>  # -> <output-dir>/vanilla-26.3.zip
+set -euo pipefail
+
+VER="${1:?usage: $0 <minecraft-version> [output-dir]}"
+OUT_DIR="$(mkdir -p "${2:-.}" && cd "${2:-.}" && pwd)"
+OUT="$OUT_DIR/vanilla-$VER.zip"
+WORK="$(mktemp -d)"
+trap 'rm -rf "$WORK"' EXIT
+
+META="$(curl -fsS https://piston-meta.mojang.com/mc/game/version_manifest_v2.json \
+  | jq -r --arg v "$VER" '.versions[] | select(.id==$v) | .url')"
+[[ -n "$META" ]] || { echo "Minecraft version $VER not found in Mojang's version manifest"; exit 1; }
+
+echo "Downloading client jar for $VER ..."
+curl -fsS -o "$WORK/client.jar" "$(curl -fsS "$META" | jq -r .downloads.client.url)"
+
+unzip -q "$WORK/client.jar" 'assets/minecraft/'{blockstates,models,textures,items,atlases,font}'/*' -d "$WORK/pack"
+rm -f "$OUT"
+(cd "$WORK/pack" && zip -qr "$OUT" .)
+echo "Wrote $OUT ($(unzip -Z1 "$OUT" | grep -vc '/$') files)"