feat: initial blog engine with multi-language, profile, and role system

- Gin + GORM + Tailwind CSS blog engine
- OS-aware config (Linux /etc/blog_go/, Windows ./win/etc/blog_go/)
- SQLite by default, MySQL support via config
- Auto-migrate database + seed admin user on first run
- Session-based auth (login/logout)
- i18n: Chinese/English with auto-detect + manual switch
- Avatar dropdown nav with click-to-toggle menu
- Profile page: avatar upload, edit info, change password
- Role system: admin (full access) and author (profile only)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

handlers/admin.go

@@ -0,0 +1,19 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// AdminDashboard renders the protected admin dashboard.
+func AdminDashboard() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		tr := getTr(c)
+		username, _ := c.Get("username")
+		data := DefaultData(c)
+		data["Title"] = tr["dash_page_title"]
+		data["Username"] = username
+		c.HTML(http.StatusOK, "dashboard", data)
+	}
+}