docs: add docker compose and buildx upgrade guide

- add a standalone docs guide for reinstalling Docker, Compose, and Buildx from the official Ubuntu repository
- refine planet.sh compose/build diagnostics so docker compose is the primary wording and missing buildx / fallback cases report more accurately
- keep the startup failure output aligned with the existing terminal tone while reducing misleading compose-version messaging

docs/docker-compose-buildx-upgrade.md

@@ -0,0 +1,105 @@
+# Docker + Compose + Buildx 升级教程
+
+流程：删除旧版 -> 安装新版 -> 验证
+
+---
+
+# 1. 删除旧版本
+
+## 删除 apt 安装的旧包
+
+```bash
+sudo apt remove -y docker.io docker-compose docker-compose-v2 docker-doc podman-docker containerd runc
+```
+
+---
+
+## 删除系统中的 `docker-compose`（V1）
+
+```bash
+sudo rm -f "$(which docker-compose 2>/dev/null)"
+```
+
+---
+
+## 查找并删除手动安装的 Buildx 插件
+
+```bash
+docker info | sed -n '/Plugins:/,/^ Server:/p' | grep -A2 buildx
+```
+
+从输出中获取 `Path`，然后执行：
+
+```bash
+rm -f <Path中对应的docker-buildx文件>
+```
+
+---
+
+## 清理无用依赖
+
+```bash
+sudo apt autoremove -y
+```
+
+---
+
+# 2. 安装 Docker 官方版本
+
+包含 Docker Engine、Docker Compose 插件、Docker Buildx 插件。
+
+## 安装依赖
+
+```bash
+sudo apt update
+sudo apt install -y ca-certificates curl gnupg
+```
+
+---
+
+## 添加 Docker GPG key
+
+```bash
+sudo install -m 0755 -d /etc/apt/keyrings
+curl -fsSL https://download.docker.com/linux/ubuntu/gpg | \
+  sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
+sudo chmod a+r /etc/apt/keyrings/docker.gpg
+```
+
+---
+
+## 添加官方仓库
+
+```bash
+echo "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
+sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
+```
+
+---
+
+## 安装 Docker + Compose + Buildx
+
+```bash
+sudo apt update
+sudo apt install -y docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
+```
+
+---
+
+# 3. 验证安装
+
+```bash
+docker --version
+docker compose version
+docker buildx version
+```
+
+---
+
+# 4. 常用命令
+
+```bash
+docker compose up -d
+docker compose down
+docker buildx build .
+```