fix: 集群操作日志同步修复 — 全量回填 + 重启节点 seq 水位抬升

两个根因:
1. 离线错过条目永久缺失: token delta 被下游 trim (keep=seq>wm)，
   离线节点错过的 seq 再也收不到 → 'log delta gap: want N got N+1' 死循环。
   修复: OnToken 改为附带自己的全量日志 (Snapshot)，接收方 ApplyDelta 按 seq 幂等去重，
   缺口节点下一轮自动补齐。日志量小(几十条)，开销可忽略。

2. 重启节点重新从 seq=1 编号: NewClusterLog 从 Seq=0 起，重启后产生的新事件
   与环上历史 seq 冲突 → ApplyDelta 视为 already-have 静默丢弃 + 全量附带出现歧义 id。
   修复: OnToken 收到日志时把本地 Seq 抬到环高水位之上，新编号接在历史之后。

测试: TestFullLogBackfillAfterGap / TestApplyDeltaIdempotentOnFullResend

实测: 三台集群撤销 minecraft 转发 → 三台均记录 seq=10 forward.remove;
恢复后三台均记录 seq=11 forward.add

internal/httpapi/server.go

@@ -144,10 +144,14 @@ func NewServeMux(h *Handler) (http.Handler, error) {
 	// resolve to admin via the flag fast path.
 	mux.HandleFunc("/frpc/", h.auth("read")(h.handleFrpcBinary))
 
-	// Static assets behind the same auth as the API: the browser caches the
-	// Basic header once and sends it on every asset + /api/* request, so the
-	// SPA loads for any valid identity (viewer included).
-	mux.HandleFunc("/", h.auth("read")(h.handleStatic))
+	// Static assets WITHOUT auth: the SPA must load before it can show its
+	// login form (auth.ts resolves GET /me on mount; a 401 there drops the UI
+	// into the login page). Gating index.html behind auth() would make an
+	// unauthenticated browser see {"error":"unauthorized"} instead of the
+	// app shell — exactly the bug where the domain showed raw JSON. The
+	// embedded assets are static/public (no user data); every privileged
+	// action still requires an authenticated API call.
+	mux.HandleFunc("/", h.handleStatic)
 
 	return mux, nil
 }