性能优化：Cesium 懒加载+后台预载、按需渲染、射线检测节流、城市标签 primitive 化、时间轴纹理跟随可视区域

- Cesium 改为动态加载（vite 插件不再注入 6MB 脚本），首屏零 Cesium 请求
- 首帧渲染后后台预载地理视图，loading 展示 8 秒期间并行，就绪前地理按钮置灰
- Three.js 按需渲染：静止停止重绘，动画/交互/状态变化时渲染
- 射线检测合帧节流，binder 只测当前页±1、时间轴只测可视窗口
- 移除 vignette 的 mix-blend-mode 全屏合成
- 7342 个城市从 entity 改为 PointPrimitiveCollection + LabelCollection
- 时间轴懒加载窗口跟随可视区域（拖拽/缩放实时跟随）

src/scene/CesiumGlobe.js

@@ -124,13 +124,20 @@ export class CesiumGlobe {
     this._visible = false;
     this._pendingData = 2; // 国家边界 + 城市数据
     this.ready = new Promise((resolve) => { this._resolveReady = resolve; });
+    this.viewerReady = new Promise((resolve) => { this._resolveViewerReady = resolve; });
   }
 
   async ensureCreated() {
     if (this._created) return;
     this._created = true;
 
-    await loadCesium();
+    try {
+      await loadCesium();
+    } catch (err) {
+      this._created = false; // 失败可重试
+      console.warn('[CesiumGlobe] Cesium 脚本加载失败：', err);
+      return;
+    }
 
     // 调整实体渲染顺序：先渲染标签（城市/国家名），再渲染 Billboard（标记便签），
     // 让词条标记始终显示在城市/国家名的上层。
@@ -255,6 +262,12 @@ export class CesiumGlobe {
     this.setVisible(this._visible);
     this.resize();
     this.flyToEntry(this.selected);
+
+    // 地球已就绪（影像/地形/城市数据继续后台加载），通知 App 隐藏加载遮罩
+    if (this._resolveViewerReady) {
+      this._resolveViewerReady();
+      this._resolveViewerReady = null;
+    }
   }
 
   _buildMarkers() {

src/scene/binder.js

@@ -5,7 +5,7 @@ import { clamp, easeOutCubic } from '../utils/easing.js';
 
 const RING_R = 0.085;
 const RING_TUBE = 0.0115;
-const STACK_GAP = 0.004;
+const STACK_GAP = 0.002;
 const PAGE_GAP = 0.02; // 页内缘离书脊的小空隙
 
 function makeLeatherTexture({ emblem = false } = {}) {
@@ -533,7 +533,7 @@ export class Binder {
   flipForward() {
     if (this.flip) this._finalizeFlip(); // 前一页没翻完也能继续翻
     if (!this.canFlipForward()) return;
-    this.flip = { index: this.current, from: 0, to: -Math.PI, t: 0, duration: 0.6 };
+    this.flip = { index: this.current, from: 0, to: -Math.PI, t: 0, duration: 0.38 };
     // 优先更新底部导航与信息卡（翻页开始即切换目标页）
     if (this.onChange) this.onChange((this.current + 1) % this.pages.length);
   }
@@ -541,7 +541,7 @@ export class Binder {
   flipBackward() {
     if (this.flip) this._finalizeFlip();
     if (!this.canFlipBackward()) return;
-    this.flip = { index: this.current - 1, from: -Math.PI, to: 0, t: 0, duration: 0.6 };
+    this.flip = { index: this.current - 1, from: -Math.PI, to: 0, t: 0, duration: 0.38 };
     // 优先更新底部导航与信息卡
     if (this.onChange) this.onChange(this.current - 1);
   }

src/scene/timeline.js

@@ -27,6 +27,7 @@ export class Timeline {
     this._visRange = null;
     this._ready = false;
     this._pending = [];
+    this._dirty = false;
 
     this._buildLine();
     this._buildCards();
@@ -141,17 +142,21 @@ export class Timeline {
       c.material.setPageMaps(this.placeholder.front, this.placeholder.back);
       c.isPlaceholder = true;
       this._textured.delete(i);
+      this._dirty = true;
     }
 
     // 进入窗口：分帧异步生成，避免一次性生成 25 页阻塞主线程
-    this._pending = [...win].filter((i) => !this._textured.has(i) && this.cards[i].isPlaceholder);
+    const next = [...win].filter((i) => !this._textured.has(i) && this.cards[i].isPlaceholder);
+    if (next.length) this._dirty = true;
+    this._pending = next;
     this.drainPending();
   }
 
   // 每帧由 App._animate 驱动，逐批生成窗口内纹理（避免阻塞）
   drainPending() {
-    if (!this._pending || !this._pending.length) return;
+    if (!this._pending || !this._pending.length) return false;
     const budget = 2; // 每帧最多生成 2 页
+    let did = false;
     for (let k = 0; k < budget && this._pending.length; k++) {
       const i = this._pending.shift();
       const c = this.cards[i];
@@ -160,7 +165,21 @@ export class Timeline {
       c.material.setPageMaps(front, back);
       c.isPlaceholder = false;
       this._textured.add(i);
+      this._dirty = true;
+      did = true;
     }
+    return did;
+  }
+
+  hasActiveFlip() {
+    return this.cards.some((c) => c.flipAnim);
+  }
+
+  // App 每帧消费“纹理窗口变化”标志，用于按需渲染
+  consumeDirty() {
+    const d = this._dirty;
+    this._dirty = false;
+    return d;
   }
 
   // 返回某张卡片在时间轴组内的横向坐标（用于点击后居中）
@@ -168,6 +187,16 @@ export class Timeline {
     return cardX(index, ENTRIES.length);
   }
 
+  // 射线检测用：只返回可视窗口内的卡片 mesh（减少求交对象）
+  pickableMeshes() {
+    if (!this._visRange) return this.cards.map((c) => c.mesh);
+    const list = [];
+    for (let i = this._visRange.min; i <= this._visRange.max; i++) {
+      if (this.cards[i]) list.push(this.cards[i].mesh);
+    }
+    return list;
+  }
+
   // 点击翻转：每次点击切换正/反面；选中另一张时，其它翻到背面的卡片先翻回正面
   flip(index) {
     this.cards.forEach((o) => {