feat: opaque session、安装/发帖 SSR 与最小 Admin 后台

浏览器登录改为 DB sessions（可吊销）；敏感词与 OIDC PEM 入 settings；
落地安装向导、注册发帖与 /admin 仪表盘/板块/审核/设置。

Co-authored-by: Cursor <cursoragent@cursor.com>

routers/web/pending.go

@@ -0,0 +1,35 @@
+package web
+
+import (
+	"net/http"
+
+	"git.iioio.com/freefire/jiang13-forum/modules/webctx"
+	"github.com/gin-gonic/gin"
+)
+
+type pendingData struct {
+	PageChrome
+	Heading string
+	Message string
+}
+
+// PendingPage 未迁移页
+func (d Deps) PendingPage(c *gin.Context) {
+	ctx := d.ctx(c)
+	chrome := d.chrome(ctx, "页面准备中 · "+d.Settings.SiteBranding().Name, "", "")
+	ctx.HTML(http.StatusOK, "status/pending", pendingData{
+		PageChrome: chrome,
+		Heading:    "页面准备中",
+		Message:    "该功能尚未用模板实现，请稍后再来。",
+	})
+}
+
+func (d Deps) render404(ctx *webctx.Context) {
+	chrome := d.chrome(ctx, "页面不存在 · "+d.Settings.SiteBranding().Name, "", "")
+	ctx.HTML(http.StatusNotFound, "status/404", chrome)
+}
+
+// NotFound NoRoute
+func (d Deps) NotFound(c *gin.Context) {
+	d.render404(d.ctx(c))
+}