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>

backend/internal/handler/public.go

@@ -2,8 +2,6 @@ package handler
 
 import (
 	"net/http"
-	"os"
-	"time"
 
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
@@ -80,23 +78,18 @@ func (h *PublicHandler) GetProduct(c *gin.Context) {
 
 // GetRelease GET /api/v1/public/release (no auth)
 func (h *PublicHandler) GetRelease(c *gin.Context) {
-	version := os.Getenv("APP_VERSION")
-	if version == "" {
-		version = "1.0.0"
+	cfg, err := loadVersionConfig()
+	if err != nil {
+		c.JSON(http.StatusOK, gin.H{
+			"version":       "1.0.0",
+			"release_notes": "",
+			"download_urls": gin.H{"web": "https://jiu.51yanmei.com/app"},
+		})
+		return
 	}
-	buildDate := os.Getenv("BUILD_DATE")
-	if buildDate == "" {
-		buildDate = time.Now().Format("2006-01-02")
-	}
-
 	c.JSON(http.StatusOK, gin.H{
-		"version":    version,
-		"build_date": buildDate,
-		"download_urls": gin.H{
-			"macos":   os.Getenv("DOWNLOAD_URL_MACOS"),
-			"windows": os.Getenv("DOWNLOAD_URL_WINDOWS"),
-			"web":     "https://jiu.51yanmei.com/app",
-		},
-		"changelog": []gin.H{},
+		"version":       cfg.Version,
+		"release_notes": cfg.ReleaseNotes,
+		"download_urls": cfg.DownloadURLs,
 	})
 }