ci: add GitHub Actions workflows to build plugin and publish releases

- build.yml: builds the shadow jar on every push/PR and uploads it as an
  artifact for verification.
- release.yml: triggered by pushing a v* tag (or manual dispatch), builds
  the plugin and attaches the shadow jar to a GitHub Release.
- fetch-libs.sh: downloads the compile-time-only jars (PlaceholderAPI,
  CMI/CMILib, HolographicDisplays, FancyHolograms, IridiumColorAPI) from
  public sources, since lib/ is gitignored.

Author: claude

.github/scripts/fetch-libs.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Downloads compile-time-only dependencies that build.gradle references via
+# `compileOnly files("lib/...")` and `implementation files("lib/...")`.
+# These jars are gitignored, so CI fetches them from public sources.
+set -euo pipefail
+
+mkdir -p lib
+cd lib
+
+fetch() {
+  local url="$1"
+  local out="$2"
+  if [ -f "$out" ]; then
+    echo "[skip] $out already present"
+    return 0
+  fi
+  echo "[get ] $out  <-  $url"
+  curl -fsSL --retry 4 --retry-delay 2 -o "$out" "$url"
+}
+
+# PlaceholderAPI
+fetch "https://repo.extendedclip.com/releases/me/clip/placeholderapi/2.11.2/placeholderapi-2.11.2.jar" \
+      "PlaceholderAPI-2.11.2.jar"
+
+# CMI + CMILib (official Zrips repo)
+fetch "https://nexus.zrips.net/repository/zrips/CMI/9.6.2.3/CMI-9.6.2.3.jar" \
+      "CMI-9.6.2.3.jar"
+fetch "https://nexus.zrips.net/repository/zrips/CMILib/1.4.0.4/CMILib-1.4.0.4.jar" \
+      "CMILib-1.4.0.4.jar"
+
+# HolographicDisplays
+fetch "https://github.com/filoghost/HolographicDisplays/releases/download/v3.0.4/HolographicDisplays-3.0.4.jar" \
+      "HolographicDisplays-3.0.4.jar"
+
+# FancyHolograms
+fetch "https://github.com/FancyMcPlugins/FancyHolograms/releases/download/v2.4.1/FancyHolograms-2.4.1.jar" \
+      "FancyHolograms-2.4.1.jar"
+
+# IridiumColorAPI (shaded into the plugin) - via jitpack
+fetch "https://jitpack.io/com/github/Iridium-Development/IridiumColorAPI/1.0.4/IridiumColorAPI-1.0.4.jar" \
+      "IridiumColorAPI-1.0.4.jar"
+
+echo "----"
+ls -la

.github/workflows/build.yml

@@ -0,0 +1,45 @@
+name: Build
+
+on:
+  push:
+    branches: [ "**" ]
+    tags-ignore: [ "v*" ]
+  pull_request:
+    branches: [ "**" ]
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - name: Set up Gradle
+        uses: gradle/actions/setup-gradle@v3
+
+      - name: Fetch compile-time libraries
+        run: bash .github/scripts/fetch-libs.sh
+
+      - name: Build with Gradle
+        run: ./gradlew clean shadowJar --no-daemon --stacktrace
+
+      - name: Read project version
+        id: version
+        run: |
+          VERSION=$(grep -E "^version" build.gradle | head -n1 | sed -E 's/.*"([^"]+)".*/\1/')
+          echo "version=$VERSION" >> "$GITHUB_OUTPUT"
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: FireMysteryBlocks-${{ steps.version.outputs.version }}
+          path: target/${{ steps.version.outputs.version }}/*.jar
+          if-no-files-found: error

.github/workflows/release.yml

@@ -0,0 +1,66 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "Release tag (e.g. v2.3.16). If empty, uses the version from build.gradle."
+        required: false
+
+permissions:
+  contents: write
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - name: Set up Gradle
+        uses: gradle/actions/setup-gradle@v3
+
+      - name: Fetch compile-time libraries
+        run: bash .github/scripts/fetch-libs.sh
+
+      - name: Build with Gradle
+        run: ./gradlew clean shadowJar --no-daemon --stacktrace
+
+      - name: Resolve version and tag
+        id: meta
+        run: |
+          PROJECT_VERSION=$(grep -E "^version" build.gradle | head -n1 | sed -E 's/.*"([^"]+)".*/\1/')
+          echo "version=$PROJECT_VERSION" >> "$GITHUB_OUTPUT"
+
+          if [ "${{ github.event_name }}" = "push" ]; then
+            TAG="${GITHUB_REF#refs/tags/}"
+          elif [ -n "${{ github.event.inputs.tag }}" ]; then
+            TAG="${{ github.event.inputs.tag }}"
+          else
+            TAG="v${PROJECT_VERSION}"
+          fi
+          echo "tag=$TAG" >> "$GITHUB_OUTPUT"
+
+      - name: List built artifacts
+        run: ls -la target/${{ steps.meta.outputs.version }}/
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          tag_name: ${{ steps.meta.outputs.tag }}
+          name: FireMysteryBlocks ${{ steps.meta.outputs.tag }}
+          generate_release_notes: true
+          draft: false
+          prerelease: false
+          files: |
+            target/${{ steps.meta.outputs.version }}/*.jar