Add dockerfile and container build

.devcontainer/devcontainer.json

@@ -0,0 +1,27 @@
+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/java
+{
+	"name": "Java",
+	// Or use a Dockerfile or Docker Compose file. More info: https://containers.dev/guide/dockerfile
+	"image": "mcr.microsoft.com/devcontainers/java:3-25-trixie",
+
+	"features": {
+		"ghcr.io/devcontainers/features/java:1": {
+			"version": "none",
+			"installMaven": "false",
+			"installGradle": "true"
+		}
+	}
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "java -version",
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}

.github/dependabot.yaml

@@ -0,0 +1,24 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for more information:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+# https://containers.dev/guide/dependabot
+
+version: 2
+updates:
+ - package-ecosystem: "devcontainers"
+   directory: "/"
+   schedule:
+     interval: weekly
+ - package-ecosystem: "gradle"
+   directory: "/"
+   schedule:
+     interval: "weekly"
+ - package-ecosystem: "docker"
+   directory: "/"
+   schedule:
+     interval: "weekly"
+ - package-ecosystem: "github-actions"
+   directory: "/"
+   schedule:
+     interval: "weekly"

.github/workflows/docker.yaml

@@ -0,0 +1,33 @@
+name: Publish Docker image
+
+on:
+  release:
+    types: [created, prereleased]
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: ./Dockerfile
+          push: true
+          tags: |
+            ghcr.io/apdevteam/modmail:${{ github.event.release.tag_name }}
+            ghcr.io/apdevteam/modmail:latest

Dockerfile

@@ -0,0 +1,9 @@
+FROM gradle:8.10-jdk25 AS build
+WORKDIR /app
+COPY . .
+RUN gradle shadowJar --no-daemon
+
+FROM eclipse-temurin:25-jre
+WORKDIR /app
+COPY --from=build /app/build/libs/ModMail.jar .
+CMD ["java", "-jar", "ModMail.jar"]

build.gradle.kts

@@ -19,7 +19,7 @@ dependencies {
 group = "io.github.apdevteam"
 version = "0.6.9"
 description = "ModMail"
-java.toolchain.languageVersion = JavaLanguageVersion.of(21)
+java.toolchain.languageVersion = JavaLanguageVersion.of(25)
 
 tasks.jar {
     manifest {