feat: 站点媒体库与移动端底部导航，服务测试补强

- 新增媒体库：media_library/media_thumbs 服务（WebP 缩略图）、管理端 media 页面
- 移动端底部导航 MobileTabBar 替换 MobilePostBar
- 旧数据导入增强与测试、路由与登录会话/板块侧边栏测试补强
- site-doc 组件精简（移除 Breadcrumb），文档新增迁移公告说明

backend/service/board_sidebar_test.go

@@ -0,0 +1,69 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/freefire/jiang13-bbs/model"
+	"github.com/glebarez/sqlite"
+	"gorm.io/gorm"
+)
+
+// 板块右栏聚合：管理员应携带等级（AfterFind 按累计积分计算）与颁发的徽章
+func TestBoardSidebarModeratorsCarryLevelAndBadges(t *testing.T) {
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.User{}, &model.Board{}, &model.UserBoard{},
+		&model.Post{}, &model.Comment{}, &model.Badge{}, &model.UserBadge{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	board := model.Board{Name: "综合讨论"}
+	if err := db.Create(&board).Error; err != nil {
+		t.Fatalf("seed board: %v", err)
+	}
+	// 高积分管理员 + 低积分管理员 + 普通用户（不入列）
+	modHigh := model.User{Username: "mod_high", Password: "x", Role: model.RoleBoardAdmin, TotalPoints: 10000}
+	modLow := model.User{Username: "mod_low", Password: "x", Role: model.RoleBoardAdmin}
+	plain := model.User{Username: "plain", Password: "x"}
+	for _, u := range []*model.User{&modHigh, &modLow, &plain} {
+		if err := db.Create(u).Error; err != nil {
+			t.Fatalf("seed user: %v", err)
+		}
+	}
+	for _, uid := range []uint{modHigh.ID, modLow.ID, plain.ID} {
+		if err := db.Create(&model.UserBoard{UserID: uid, BoardID: board.ID}).Error; err != nil {
+			t.Fatalf("seed user_board: %v", err)
+		}
+	}
+	badge := model.Badge{Name: "骨灰玩家", Icon: "medal", Color: "gold"}
+	if err := db.Create(&badge).Error; err != nil {
+		t.Fatalf("seed badge: %v", err)
+	}
+	if err := db.Create(&model.UserBadge{BadgeID: badge.ID, UserID: modHigh.ID, AwardedBy: 1}).Error; err != nil {
+		t.Fatalf("seed user_badge: %v", err)
+	}
+
+	s := NewBoardService(db)
+	data, err := s.Sidebar(board.ID)
+	if err != nil {
+		t.Fatalf("Sidebar: %v", err)
+	}
+	if len(data.Moderators) != 2 {
+		t.Fatalf("应只含 2 名 board_admin，got %d", len(data.Moderators))
+	}
+	first := data.Moderators[0]
+	if first.Username != "mod_high" {
+		t.Fatalf("排序错位: %+v", first)
+	}
+	if first.Level <= 1 {
+		t.Fatalf("高积分管理员等级应 >1，got %d", first.Level)
+	}
+	if len(first.Badges) != 1 || first.Badges[0].Badge.Name != "骨灰玩家" {
+		t.Fatalf("徽章未随行加载: %+v", first.Badges)
+	}
+	if data.Moderators[1].Level != 1 || len(data.Moderators[1].Badges) != 0 {
+		t.Fatalf("低积分管理员应为 Lv.1 无徽章: %+v", data.Moderators[1])
+	}
+}