Add CI workflows

.github/workflows/main.yml

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+name: Main
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+  workflow_run:
+    types:
+      - completed
+    workflows:
+      - "Update WIT"
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  main:
+    name: Build, test, and release
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+        with:
+          submodules: true
+
+      - name: Set up Java/Kotlin
+        uses: actions/setup-java@v6
+        with:
+          distribution: liberica
+          java-version: "25"
+
+      - name: Build example plugin to test
+        run: |
+          ./gradlew build --no-daemon

.github/workflows/update-wit.yml

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+name: Update WIT
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: write
+
+jobs:
+  update-wit:
+    name: Update WIT
+    runs-on: ubuntu-slim
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+        with:
+          submodules: true
+      - name: Update submodule
+        id: update_submodule
+        run: |
+          set -eux
+
+          cd wit
+          git fetch origin master
+          git checkout FETCH_HEAD
+
+          echo "wit_commit=$(git rev-parse --short HEAD)" >> $GITHUB_OUTPUT
+
+      - name: Commit
+        run: |
+          set -eux
+
+          witCommit='${{ steps.update_submodule.outputs.wit_commit }}'
+
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+
+          git add wit
+          git commit -m "Sync to Pumpkin-MC/pumpkin-plugin-wit@${witCommit}"
+          git push