feat: 官网 + 管理端 + Gin/GORM 后端首个完整版本

- web/: 产品官网（Hero 事件流终端、功能矩阵、架构、快速开始、下载、博客 + Markdown 详情页），青瓷绿双主题
- admin/: 内容管理（JWT 登录、文章分页/搜索/CRUD、草稿与发布），embed 挂 /admin
- server/: Gin + GORM，MySQL（DSN 走 .env，SQLite 兜底）；规范落地：sundynix_ 表前缀、字符串雪花主键、snake_case 列名、统一响应信封、公共分页参数
- 双 SPA embed 单二进制部署，make build 一键出包

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/middleware/auth.go

@@ -0,0 +1,29 @@
+package middleware
+
+import (
+	"strings"
+
+	"github.com/gin-gonic/gin"
+
+	"git.sundynix.cn/Blizzard/sundynix-site/server/internal/pkg/auth"
+	"git.sundynix.cn/Blizzard/sundynix-site/server/internal/pkg/resp"
+)
+
+// Auth 校验 Authorization: Bearer <token>，通过后把用户名放进上下文。
+func Auth() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		h := c.GetHeader("Authorization")
+		token, ok := strings.CutPrefix(h, "Bearer ")
+		if !ok || token == "" {
+			resp.Unauthorized(c, "未登录")
+			return
+		}
+		username, err := auth.Parse(token)
+		if err != nil {
+			resp.Unauthorized(c, err.Error())
+			return
+		}
+		c.Set("username", username)
+		c.Next()
+	}
+}

server/internal/middleware/cors.go

@@ -0,0 +1,24 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// CORS 开发期跨域放行；生产同源部署（embed）时不会触发预检。
+func CORS() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		origin := c.GetHeader("Origin")
+		if origin != "" {
+			c.Header("Access-Control-Allow-Origin", origin)
+			c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
+			c.Header("Access-Control-Allow-Headers", "Content-Type, Authorization")
+		}
+		if c.Request.Method == http.MethodOptions {
+			c.AbortWithStatus(http.StatusNoContent)
+			return
+		}
+		c.Next()
+	}
+}