feat: add Gitea Action Runner base and Java images

- gitea_runner_base: base image with common build tools (git, curl, wget, tar, etc.)
- gitea_runner_java: Java image with JDK 7/8/11/17/21 and Maven 3.9.9
- Update README with build instructions and usage examples

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

gitea_runner_base/Dockerfile

@@ -0,0 +1,38 @@
+# Gitea Action Runner Base Image
+# 基于 gitea/act_runner 添加常用构建工具，不含具体语言环境
+
+FROM gitea/act_runner:latest
+
+LABEL maintainer="www.imyeyu.com"
+LABEL description="Gitea Action Runner with basic build tools"
+
+# 安装基本构建工具
+# act_runner 基于 Alpine Linux
+RUN apk update && apk add --no-cache \
+    # 版本控制
+    git \
+    git-lfs \
+    # 网络工具
+    curl \
+    wget \
+    ca-certificates \
+    openssl \
+    # 压缩/解压工具
+    tar \
+    gzip \
+    bzip2 \
+    xz \
+    zip \
+    unzip \
+    # 基本构建工具
+    make \
+    bash \
+    coreutils \
+    findutils \
+    grep \
+    sed \
+    gawk \
+    # 其他常用工具
+    jq \
+    tree \
+    && rm -rf /var/cache/apk/*