refactor: modular init, add bedrock loader, dynamic java/healthcheck

- Split monolithic init into modular lib files under scripts/lib/
  (common.sh, java.sh, server.sh, loaders/{vanilla,paper,fabric,forge,neoforge}.sh)
- Add bedrock loader: downloads from Minecraft Services API,
  runs native binary with LD_LIBRARY_PATH, skips Java setup
- Add auto-detection for JAVA_VERSION from Mojang version manifest
  (MC 1.20.5+ -> temurin@21, 1.17-1.20.4 -> temurin@17,
   1.17 -> temurin@16, pre-1.17 -> temurin@8)
- Fix NEW_FORGE unbound variable when non-Forge loaders run
- Fix Fabric loader jq filter (-s slurp removed, null string check fixed)
- Fix Forge test detection (recursive find for forge-*-server.jar)
- Dynamic healthcheck: nc -z TCP 25565 for Java, nc -zu UDP 19132 for bedrock
- Add .gitea/workflows/build-dev.yml for dev branch CI builds
- Base image: debian:bookworm-slim (from ubuntu:noble)
- Add unzip, netcat-openbsd to Docker image
- Switch to shebangs, set -euo pipefail throughout

scripts/lib/loaders/vanilla.sh

@@ -0,0 +1,13 @@
+getVanilla() {
+  SERVER_TYPE="Vanilla Minecraft"
+  MANIFEST=$(curl -s https://launchermeta.mojang.com/mc/game/version_manifest.json)
+  VERSION_URL=$(echo "$MANIFEST" | jq -r ".versions[] | select(.id == \"${MC_VERSION}\") | .url")
+  if [[ -n "$VERSION_URL" ]] && [[ "$VERSION_URL" != "null" ]]; then
+    VERSION_DATA=$(curl -s "$VERSION_URL")
+    DOWNLOAD_URL=$(echo "$VERSION_DATA" | jq -r ".downloads.server.url")
+    curl -o server.jar "$DOWNLOAD_URL"
+  else
+    echo "Version ${MC_VERSION} not found in Mojang manifest"
+    crash
+  fi
+}