feat(deploy): SemVer 版本管理 + 自动化发版流水线

- deploy.yml: tag 触发（v*.*.*），四阶段调脚本（compile/test/release/deploy）
- manual.yml: workflow_dispatch 支持手动回滚，checkout 指定 tag
- scripts/ci/compile.sh: 构建 Go 二进制 + Flutter Web，打包 dist/
- scripts/ci/test.sh: go test + flutter analyze
- scripts/ci/release.sh: 解析 CHANGELOG.md → 更新 version.yaml → 创建 Forgejo Release
- scripts/ci/deploy.sh: 从 Release 下载产物（自动/手动均可）→ 部署到 EC2
- CHANGELOG.md: Keep a Changelog 格式，初始 v1.0.0 条目
- backend: GetRelease 改读 version.yaml，移除 ENV 变量依赖
- backend/config/version.yaml: 重置为 v1.0.0
- web/download.html: 动态拉取 /api/v1/public/release 展示版本号和更新内容

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitea/workflows/manual.yml

@@ -0,0 +1,28 @@
+name: Manual Deploy
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Tag to deploy (e.g. v1.0.0)'
+        required: true
+        type: string
+
+jobs:
+  deploy:
+    runs-on: mac
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.version }}
+
+      - name: Deploy
+        env:
+          FORGEJO_TOKEN: ${{ secrets.FORGEJO_TOKEN }}
+          FORGEJO_URL: ${{ secrets.FORGEJO_URL }}
+          GITEA_REPOSITORY: ${{ gitea.repository }}
+          EC2_SSH_KEY: ${{ secrets.EC2_SSH_KEY }}
+          EC2_HOST: ${{ secrets.EC2_HOST }}
+          EC2_USER: ${{ secrets.EC2_USER }}
+        run: sh scripts/ci/deploy.sh "${{ inputs.version }}"