release automation: gitea actions build every push and publish tagged releases (version from the tag, packages, sha256sums, changelog section as text), simple 5-step install guide in the readme

.gitea/workflows/build.yml

@@ -0,0 +1,25 @@
+# Builds and tests every push and pull request (tests that need the game CD skip themselves).
+name: build
+
+on:
+  push:
+    branches: ['**']
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: |
+            25
+            21
+      - name: Build and test
+        run: |
+          ./gradlew --no-daemon \
+            -Porg.gradle.java.installations.fromEnv=JAVA_HOME_25_X64 \
+            -Porg.gradle.java.installations.auto-download=false \
+            build